MCL/sf/app/podcatcher: comparison engine/sqlite/src/where.cpp

equal deleted inserted replaced

-:5f8e5adbbed9
+:29cda98b007e
+/*
+** 2001 September 15
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+** This module contains C code that generates VDBE code used to process
+** the WHERE clause of SQL statements.  This module is reponsible for
+** generating the code that loops through a table looking for applicable
+** rows.  Indices are selected and used to speed the search when doing
+** so is applicable.  Because this module is responsible for selecting
+** indices, you might also think of this module as the "query optimizer".
+**
+** $Id: where.cpp 1282 2008-11-13 09:31:33Z LarsPson $
+*/
+#include "sqliteInt.h"
+/*
+** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
+*/
+#define BMS  (sizeof(Bitmask)*8)
+/*
+** Trace output macros
+*/
+#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
+int sqlite3_where_trace = 0;
+# define WHERETRACE(X)  if(sqlite3_where_trace) sqlite3DebugPrintf X
+#else
+# define WHERETRACE(X)
+#endif
+/* Forward reference
+*/
+typedef struct WhereClause WhereClause;
+typedef struct ExprMaskSet ExprMaskSet;
+/*
+** The query generator uses an array of instances of this structure to
+** help it analyze the subexpressions of the WHERE clause.  Each WHERE
+** clause subexpression is separated from the others by an AND operator.
+**
+** All WhereTerms are collected into a single WhereClause structure.
+** The following identity holds:
+**
+**        WhereTerm.pWC->a[WhereTerm.idx] == WhereTerm
+**
+** When a term is of the form:
+**
+**              X <op> <expr>
+**
+** where X is a column name and <op> is one of certain operators,
+** then WhereTerm.leftCursor and WhereTerm.leftColumn record the
+** cursor number and column number for X.  WhereTerm.operator records
+** the <op> using a bitmask encoding defined by WO_xxx below.  The
+** use of a bitmask encoding for the operator allows us to search
+** quickly for terms that match any of several different operators.
+**
+** prereqRight and prereqAll record sets of cursor numbers,
+** but they do so indirectly.  A single ExprMaskSet structure translates
+** cursor number into bits and the translated bit is stored in the prereq
+** fields.  The translation is used in order to maximize the number of
+** bits that will fit in a Bitmask.  The VDBE cursor numbers might be
+** spread out over the non-negative integers.  For example, the cursor
+** numbers might be 3, 8, 9, 10, 20, 23, 41, and 45.  The ExprMaskSet
+** translates these sparse cursor numbers into consecutive integers
+** beginning with 0 in order to make the best possible use of the available
+** bits in the Bitmask.  So, in the example above, the cursor numbers
+** would be mapped into integers 0 through 7.
+*/
+typedef struct WhereTerm WhereTerm;
+struct WhereTerm {
+Expr *pExpr;            /* Pointer to the subexpression */
+i16 iParent;            /* Disable pWC->a[iParent] when this term disabled */
+i16 leftCursor;         /* Cursor number of X in "X <op> <expr>" */
+i16 leftColumn;         /* Column number of X in "X <op> <expr>" */
+u16 eOperator;          /* A WO_xx value describing <op> */
+u8 flags;               /* Bit flags.  See below */
+u8 nChild;              /* Number of children that must disable us */
+WhereClause *pWC;       /* The clause this term is part of */
+Bitmask prereqRight;    /* Bitmask of tables used by pRight */
+Bitmask prereqAll;      /* Bitmask of tables referenced by p */
+};
+/*
+** Allowed values of WhereTerm.flags
+*/
+#define TERM_DYNAMIC    0x01   /* Need to call sqlite3ExprDelete(pExpr) */
+#define TERM_VIRTUAL    0x02   /* Added by the optimizer.  Do not code */
+#define TERM_CODED      0x04   /* This term is already coded */
+#define TERM_COPIED     0x08   /* Has a child */
+#define TERM_OR_OK      0x10   /* Used during OR-clause processing */
+/*
+** An instance of the following structure holds all information about a
+** WHERE clause.  Mostly this is a container for one or more WhereTerms.
+*/
+struct WhereClause {
+Parse *pParse;           /* The parser context */
+ExprMaskSet *pMaskSet;   /* Mapping of table indices to bitmasks */
+int nTerm;               /* Number of terms */
+int nSlot;               /* Number of entries in a[] */
+WhereTerm *a;            /* Each a[] describes a term of the WHERE cluase */
+WhereTerm aStatic[10];   /* Initial static space for a[] */
+};
+/*
+** An instance of the following structure keeps track of a mapping
+** between VDBE cursor numbers and bits of the bitmasks in WhereTerm.
+**
+** The VDBE cursor numbers are small integers contained in
+** SrcList_item.iCursor and Expr.iTable fields.  For any given WHERE
+** clause, the cursor numbers might not begin with 0 and they might
+** contain gaps in the numbering sequence.  But we want to make maximum
+** use of the bits in our bitmasks.  This structure provides a mapping
+** from the sparse cursor numbers into consecutive integers beginning
+** with 0.
+**
+** If ExprMaskSet.ix[A]==B it means that The A-th bit of a Bitmask
+** corresponds VDBE cursor number B.  The A-th bit of a bitmask is 1<<A.
+**
+** For example, if the WHERE clause expression used these VDBE
+** cursors:  4, 5, 8, 29, 57, 73.  Then the  ExprMaskSet structure
+** would map those cursor numbers into bits 0 through 5.
+**
+** Note that the mapping is not necessarily ordered.  In the example
+** above, the mapping might go like this:  4->3, 5->1, 8->2, 29->0,
+** 57->5, 73->4.  Or one of 719 other combinations might be used. It
+** does not really matter.  What is important is that sparse cursor
+** numbers all get mapped into bit numbers that begin with 0 and contain
+** no gaps.
+*/
+struct ExprMaskSet {
+int n;                        /* Number of assigned cursor values */
+int ix[sizeof(Bitmask)*8];    /* Cursor assigned to each bit */
+};
+/*
+** Bitmasks for the operators that indices are able to exploit.  An
+** OR-ed combination of these values can be used when searching for
+** terms in the where clause.
+*/
+#define WO_IN     1
+#define WO_EQ     2
+#define WO_LT     (WO_EQ<<(TK_LT-TK_EQ))
+#define WO_LE     (WO_EQ<<(TK_LE-TK_EQ))
+#define WO_GT     (WO_EQ<<(TK_GT-TK_EQ))
+#define WO_GE     (WO_EQ<<(TK_GE-TK_EQ))
+#define WO_MATCH  64
+#define WO_ISNULL 128
+/*
+** Value for flags returned by bestIndex().
+**
+** The least significant byte is reserved as a mask for WO_ values above.
+** The WhereLevel.flags field is usually set to WO_IN|WO_EQ|WO_ISNULL.
+** But if the table is the right table of a left join, WhereLevel.flags
+** is set to WO_IN|WO_EQ.  The WhereLevel.flags field can then be used as
+** the "op" parameter to findTerm when we are resolving equality constraints.
+** ISNULL constraints will then not be used on the right table of a left
+** join.  Tickets #2177 and #2189.
+*/
+#define WHERE_ROWID_EQ     0x000100   /* rowid=EXPR or rowid IN (...) */
+#define WHERE_ROWID_RANGE  0x000200   /* rowid<EXPR and/or rowid>EXPR */
+#define WHERE_COLUMN_EQ    0x001000   /* x=EXPR or x IN (...) */
+#define WHERE_COLUMN_RANGE 0x002000   /* x<EXPR and/or x>EXPR */
+#define WHERE_COLUMN_IN    0x004000   /* x IN (...) */
+#define WHERE_TOP_LIMIT    0x010000   /* x<EXPR or x<=EXPR constraint */
+#define WHERE_BTM_LIMIT    0x020000   /* x>EXPR or x>=EXPR constraint */
+#define WHERE_IDX_ONLY     0x080000   /* Use index only - omit table */
+#define WHERE_ORDERBY      0x100000   /* Output will appear in correct order */
+#define WHERE_REVERSE      0x200000   /* Scan in reverse order */
+#define WHERE_UNIQUE       0x400000   /* Selects no more than one row */
+#define WHERE_VIRTUALTABLE 0x800000   /* Use virtual-table processing */
+/*
+** Initialize a preallocated WhereClause structure.
+*/
+static void whereClauseInit(
+WhereClause *pWC,        /* The WhereClause to be initialized */
+Parse *pParse,           /* The parsing context */
+ExprMaskSet *pMaskSet    /* Mapping from table indices to bitmasks */
+){
+pWC->pParse = pParse;
+pWC->pMaskSet = pMaskSet;
+pWC->nTerm = 0;
+pWC->nSlot = ArraySize(pWC->aStatic);
+pWC->a = pWC->aStatic;
+}
+/*
+** Deallocate a WhereClause structure.  The WhereClause structure
+** itself is not freed.  This routine is the inverse of whereClauseInit().
+*/
+static void whereClauseClear(WhereClause *pWC){
+int i;
+WhereTerm *a;
+for(i=pWC->nTerm-1, a=pWC->a; i>=0; i--, a++){
+if( a->flags & TERM_DYNAMIC ){
+sqlite3ExprDelete(a->pExpr);
+}
+}
+if( pWC->a!=pWC->aStatic ){
+sqlite3_free(pWC->a);
+}
+}
+/*
+** Add a new entries to the WhereClause structure.  Increase the allocated
+** space as necessary.
+**
+** If the flags argument includes TERM_DYNAMIC, then responsibility
+** for freeing the expression p is assumed by the WhereClause object.
+**
+** WARNING:  This routine might reallocate the space used to store
+** WhereTerms.  All pointers to WhereTerms should be invalided after
+** calling this routine.  Such pointers may be reinitialized by referencing
+** the pWC->a[] array.
+*/
+static int whereClauseInsert(WhereClause *pWC, Expr *p, int flags){
+WhereTerm *pTerm;
+int idx;
+if( pWC->nTerm>=pWC->nSlot ){
+WhereTerm *pOld = pWC->a;
+pWC->a = (WhereTerm*)sqlite3_malloc( sizeof(pWC->a[0])*pWC->nSlot*2 );
+if( pWC->a==0 ){
+pWC->pParse->db->mallocFailed = 1;
+if( flags & TERM_DYNAMIC ){
+sqlite3ExprDelete(p);
+}
+pWC->a = pOld;
+return 0;
+}
+memcpy(pWC->a, pOld, sizeof(pWC->a[0])*pWC->nTerm);
+if( pOld!=pWC->aStatic ){
+sqlite3_free(pOld);
+}
+pWC->nSlot *= 2;
+}
+pTerm = &pWC->a[idx = pWC->nTerm];
+pWC->nTerm++;
+pTerm->pExpr = p;
+pTerm->flags = flags;
+pTerm->pWC = pWC;
+pTerm->iParent = -1;
+return idx;
+}
+/*
+** This routine identifies subexpressions in the WHERE clause where
+** each subexpression is separated by the AND operator or some other
+** operator specified in the op parameter.  The WhereClause structure
+** is filled with pointers to subexpressions.  For example:
+**
+**    WHERE  a=='hello' AND coalesce(b,11)<10 AND (c+12!=d OR c==22)
+**           \________/     \_______________/     \________________/
+**            slot[0]            slot[1]               slot[2]
+**
+** The original WHERE clause in pExpr is unaltered.  All this routine
+** does is make slot[] entries point to substructure within pExpr.
+**
+** In the previous sentence and in the diagram, "slot[]" refers to
+** the WhereClause.a[] array.  This array grows as needed to contain
+** all terms of the WHERE clause.
+*/
+static void whereSplit(WhereClause *pWC, Expr *pExpr, int op){
+if( pExpr==0 ) return;
+if( pExpr->op!=op ){
+whereClauseInsert(pWC, pExpr, 0);
+}else{
+whereSplit(pWC, pExpr->pLeft, op);
+whereSplit(pWC, pExpr->pRight, op);
+}
+}
+/*
+** Initialize an expression mask set
+*/
+#define initMaskSet(P)  memset(P, 0, sizeof(*P))
+/*
+** Return the bitmask for the given cursor number.  Return 0 if
+** iCursor is not in the set.
+*/
+static Bitmask getMask(ExprMaskSet *pMaskSet, int iCursor){
+int i;
+for(i=0; i<pMaskSet->n; i++){
+if( pMaskSet->ix[i]==iCursor ){
+return ((Bitmask)1)<<i;
+}
+}
+return 0;
+}
+/*
+** Create a new mask for cursor iCursor.
+**
+** There is one cursor per table in the FROM clause.  The number of
+** tables in the FROM clause is limited by a test early in the
+** sqlite3WhereBegin() routine.  So we know that the pMaskSet->ix[]
+** array will never overflow.
+*/
+static void createMask(ExprMaskSet *pMaskSet, int iCursor){
+assert( pMaskSet->n < ArraySize(pMaskSet->ix) );
+pMaskSet->ix[pMaskSet->n++] = iCursor;
+}
+/*
+** This routine walks (recursively) an expression tree and generates
+** a bitmask indicating which tables are used in that expression
+** tree.
+**
+** In order for this routine to work, the calling function must have
+** previously invoked sqlite3ExprResolveNames() on the expression.  See
+** the header comment on that routine for additional information.
+** The sqlite3ExprResolveNames() routines looks for column names and
+** sets their opcodes to TK_COLUMN and their Expr.iTable fields to
+** the VDBE cursor number of the table.  This routine just has to
+** translate the cursor numbers into bitmask values and OR all
+** the bitmasks together.
+*/
+static Bitmask exprListTableUsage(ExprMaskSet*, ExprList*);
+static Bitmask exprSelectTableUsage(ExprMaskSet*, Select*);
+static Bitmask exprTableUsage(ExprMaskSet *pMaskSet, Expr *p){
+Bitmask mask = 0;
+if( p==0 ) return 0;
+if( p->op==TK_COLUMN ){
+mask = getMask(pMaskSet, p->iTable);
+return mask;
+}
+mask = exprTableUsage(pMaskSet, p->pRight);
+mask |= exprTableUsage(pMaskSet, p->pLeft);
+mask |= exprListTableUsage(pMaskSet, p->pList);
+mask |= exprSelectTableUsage(pMaskSet, p->pSelect);
+return mask;
+}
+static Bitmask exprListTableUsage(ExprMaskSet *pMaskSet, ExprList *pList){
+int i;
+Bitmask mask = 0;
+if( pList ){
+for(i=0; i<pList->nExpr; i++){
+mask |= exprTableUsage(pMaskSet, pList->a[i].pExpr);
+}
+}
+return mask;
+}
+static Bitmask exprSelectTableUsage(ExprMaskSet *pMaskSet, Select *pS){
+Bitmask mask = 0;
+while( pS ){
+mask |= exprListTableUsage(pMaskSet, pS->pEList);
+mask |= exprListTableUsage(pMaskSet, pS->pGroupBy);
+mask |= exprListTableUsage(pMaskSet, pS->pOrderBy);
+mask |= exprTableUsage(pMaskSet, pS->pWhere);
+mask |= exprTableUsage(pMaskSet, pS->pHaving);
+pS = pS->pPrior;
+}
+return mask;
+}
+/*
+** Return TRUE if the given operator is one of the operators that is
+** allowed for an indexable WHERE clause term.  The allowed operators are
+** "=", "<", ">", "<=", ">=", and "IN".
+*/
+static int allowedOp(int op){
+assert( TK_GT>TK_EQ && TK_GT<TK_GE );
+assert( TK_LT>TK_EQ && TK_LT<TK_GE );
+assert( TK_LE>TK_EQ && TK_LE<TK_GE );
+assert( TK_GE==TK_EQ+4 );
+return op==TK_IN || (op>=TK_EQ && op<=TK_GE) || op==TK_ISNULL;
+}
+/*
+** Swap two objects of type T.
+*/
+#define SWAP(TYPE,A,B) {TYPE t=A; A=B; B=t;}
+/*
+** Commute a comparision operator.  Expressions of the form "X op Y"
+** are converted into "Y op X".
+**
+** If a collation sequence is associated with either the left or right
+** side of the comparison, it remains associated with the same side after
+** the commutation. So "Y collate NOCASE op X" becomes
+** "X collate NOCASE op Y". This is because any collation sequence on
+** the left hand side of a comparison overrides any collation sequence
+** attached to the right. For the same reason the EP_ExpCollate flag
+** is not commuted.
+*/
+static void exprCommute(Expr *pExpr){
+u16 expRight = (pExpr->pRight->flags & EP_ExpCollate);
+u16 expLeft = (pExpr->pLeft->flags & EP_ExpCollate);
+assert( allowedOp(pExpr->op) && pExpr->op!=TK_IN );
+SWAP(CollSeq*,pExpr->pRight->pColl,pExpr->pLeft->pColl);
+pExpr->pRight->flags = (pExpr->pRight->flags & ~EP_ExpCollate) | expLeft;
+pExpr->pLeft->flags = (pExpr->pLeft->flags & ~EP_ExpCollate) | expRight;
+SWAP(Expr*,pExpr->pRight,pExpr->pLeft);
+if( pExpr->op>=TK_GT ){
+assert( TK_LT==TK_GT+2 );
+assert( TK_GE==TK_LE+2 );
+assert( TK_GT>TK_EQ );
+assert( TK_GT<TK_LE );
+assert( pExpr->op>=TK_GT && pExpr->op<=TK_GE );
+pExpr->op = ((pExpr->op-TK_GT)^2)+TK_GT;
+}
+}
+/*
+** Translate from TK_xx operator to WO_xx bitmask.
+*/
+static int operatorMask(int op){
+int c;
+assert( allowedOp(op) );
+if( op==TK_IN ){
+c = WO_IN;
+}else if( op==TK_ISNULL ){
+c = WO_ISNULL;
+}else{
+c = WO_EQ<<(op-TK_EQ);
+}
+assert( op!=TK_ISNULL || c==WO_ISNULL );
+assert( op!=TK_IN || c==WO_IN );
+assert( op!=TK_EQ || c==WO_EQ );
+assert( op!=TK_LT || c==WO_LT );
+assert( op!=TK_LE || c==WO_LE );
+assert( op!=TK_GT || c==WO_GT );
+assert( op!=TK_GE || c==WO_GE );
+return c;
+}
+/*
+** Search for a term in the WHERE clause that is of the form "X <op> <expr>"
+** where X is a reference to the iColumn of table iCur and <op> is one of
+** the WO_xx operator codes specified by the op parameter.
+** Return a pointer to the term.  Return 0 if not found.
+*/
+static WhereTerm *findTerm(
+WhereClause *pWC,     /* The WHERE clause to be searched */
+int iCur,             /* Cursor number of LHS */
+int iColumn,          /* Column number of LHS */
+Bitmask notReady,     /* RHS must not overlap with this mask */
+u16 op,               /* Mask of WO_xx values describing operator */
+Index *pIdx           /* Must be compatible with this index, if not NULL */
+){
+WhereTerm *pTerm;
+int k;
+for(pTerm=pWC->a, k=pWC->nTerm; k; k--, pTerm++){
+if( pTerm->leftCursor==iCur
+&& (pTerm->prereqRight & notReady)==0
+&& pTerm->leftColumn==iColumn
+&& (pTerm->eOperator & op)!=0
+){
+if( iCur>=0 && pIdx && pTerm->eOperator!=WO_ISNULL ){
+Expr *pX = pTerm->pExpr;
+CollSeq *pColl;
+char idxaff;
+int j;
+Parse *pParse = pWC->pParse;
+idxaff = pIdx->pTable->aCol[iColumn].affinity;
+if( !sqlite3IndexAffinityOk(pX, idxaff) ) continue;
+/* Figure out the collation sequence required from an index for
+** it to be useful for optimising expression pX. Store this
+** value in variable pColl.
+*/
+assert(pX->pLeft);
+pColl = sqlite3BinaryCompareCollSeq(pParse, pX->pLeft, pX->pRight);
+if( !pColl ){
+pColl = pParse->db->pDfltColl;
+}
+for(j=0; j<pIdx->nColumn && pIdx->aiColumn[j]!=iColumn; j++){}
+assert( j<pIdx->nColumn );
+if( sqlite3StrICmp(pColl->zName, pIdx->azColl[j]) ) continue;
+}
+return pTerm;
+}
+}
+return 0;
+}
+/* Forward reference */
+static void exprAnalyze(SrcList*, WhereClause*, int);
+/*
+** Call exprAnalyze on all terms in a WHERE clause.
+**
+**
+*/
+static void exprAnalyzeAll(
+SrcList *pTabList,       /* the FROM clause */
+WhereClause *pWC         /* the WHERE clause to be analyzed */
+){
+int i;
+for(i=pWC->nTerm-1; i>=0; i--){
+exprAnalyze(pTabList, pWC, i);
+}
+}
+#ifndef SQLITE_OMIT_LIKE_OPTIMIZATION
+/*
+** Check to see if the given expression is a LIKE or GLOB operator that
+** can be optimized using inequality constraints.  Return TRUE if it is
+** so and false if not.
+**
+** In order for the operator to be optimizible, the RHS must be a string
+** literal that does not begin with a wildcard.
+*/
+static int isLikeOrGlob(
+sqlite3 *db,      /* The database */
+Expr *pExpr,      /* Test this expression */
+int *pnPattern,   /* Number of non-wildcard prefix characters */
+int *pisComplete  /* True if the only wildcard is % in the last character */
+){
+const char *z;
+Expr *pRight, *pLeft;
+ExprList *pList;
+int c, cnt;
+int noCase;
+char wc[3];
+CollSeq *pColl;
+if( !sqlite3IsLikeFunction(db, pExpr, &noCase, wc) ){
+return 0;
+}
+pList = pExpr->pList;
+pRight = pList->a[0].pExpr;
+if( pRight->op!=TK_STRING ){
+return 0;
+}
+pLeft = pList->a[1].pExpr;
+if( pLeft->op!=TK_COLUMN ){
+return 0;
+}
+pColl = pLeft->pColl;
+if( pColl==0 ){
+/* TODO: Coverage testing doesn't get this case. Is it actually possible
+** for an expression of type TK_COLUMN to not have an assigned collation
+** sequence at this point?
+*/
+pColl = db->pDfltColl;
+}
+if( (pColl->type!=SQLITE_COLL_BINARY || noCase) &&
+(pColl->type!=SQLITE_COLL_NOCASE || !noCase) ){
+return 0;
+}
+sqlite3DequoteExpr(db, pRight);
+z = (char *)pRight->token.z;
+cnt = 0;
+if( z ){
+while( (c=z[cnt])!=0 && c!=wc[0] && c!=wc[1] && c!=wc[2] ){ cnt++; }
+}
+if( cnt==0 || 255==(u8)z[cnt] ){
+return 0;
+}
+*pisComplete = z[cnt]==wc[0] && z[cnt+1]==0;
+*pnPattern = cnt;
+return 1;
+}
+#endif /* SQLITE_OMIT_LIKE_OPTIMIZATION */
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+/*
+** Check to see if the given expression is of the form
+**
+**         column MATCH expr
+**
+** If it is then return TRUE.  If not, return FALSE.
+*/
+static int isMatchOfColumn(
+Expr *pExpr      /* Test this expression */
+){
+ExprList *pList;
+if( pExpr->op!=TK_FUNCTION ){
+return 0;
+}
+if( pExpr->token.n!=5 ||
+sqlite3StrNICmp((const char*)pExpr->token.z,"match",5)!=0 ){
+return 0;
+}
+pList = pExpr->pList;
+if( pList->nExpr!=2 ){
+return 0;
+}
+if( pList->a[1].pExpr->op != TK_COLUMN ){
+return 0;
+}
+return 1;
+}
+#endif /* SQLITE_OMIT_VIRTUALTABLE */
+/*
+** If the pBase expression originated in the ON or USING clause of
+** a join, then transfer the appropriate markings over to derived.
+*/
+static void transferJoinMarkings(Expr *pDerived, Expr *pBase){
+pDerived->flags |= pBase->flags & EP_FromJoin;
+pDerived->iRightJoinTable = pBase->iRightJoinTable;
+}
+#if !defined(SQLITE_OMIT_OR_OPTIMIZATION) && !defined(SQLITE_OMIT_SUBQUERY)
+/*
+** Return TRUE if the given term of an OR clause can be converted
+** into an IN clause.  The iCursor and iColumn define the left-hand
+** side of the IN clause.
+**
+** The context is that we have multiple OR-connected equality terms
+** like this:
+**
+**           a=<expr1> OR  a=<expr2> OR b=<expr3>  OR ...
+**
+** The pOrTerm input to this routine corresponds to a single term of
+** this OR clause.  In order for the term to be a condidate for
+** conversion to an IN operator, the following must be true:
+**
+**     *  The left-hand side of the term must be the column which
+**        is identified by iCursor and iColumn.
+**
+**     *  If the right-hand side is also a column, then the affinities
+**        of both right and left sides must be such that no type
+**        conversions are required on the right.  (Ticket #2249)
+**
+** If both of these conditions are true, then return true.  Otherwise
+** return false.
+*/
+static int orTermIsOptCandidate(WhereTerm *pOrTerm, int iCursor, int iColumn){
+int affLeft, affRight;
+assert( pOrTerm->eOperator==WO_EQ );
+if( pOrTerm->leftCursor!=iCursor ){
+return 0;
+}
+if( pOrTerm->leftColumn!=iColumn ){
+return 0;
+}
+affRight = sqlite3ExprAffinity(pOrTerm->pExpr->pRight);
+if( affRight==0 ){
+return 1;
+}
+affLeft = sqlite3ExprAffinity(pOrTerm->pExpr->pLeft);
+if( affRight!=affLeft ){
+return 0;
+}
+return 1;
+}
+/*
+** Return true if the given term of an OR clause can be ignored during
+** a check to make sure all OR terms are candidates for optimization.
+** In other words, return true if a call to the orTermIsOptCandidate()
+** above returned false but it is not necessary to disqualify the
+** optimization.
+**
+** Suppose the original OR phrase was this:
+**
+**           a=4  OR  a=11  OR  a=b
+**
+** During analysis, the third term gets flipped around and duplicate
+** so that we are left with this:
+**
+**           a=4  OR  a=11  OR  a=b  OR  b=a
+**
+** Since the last two terms are duplicates, only one of them
+** has to qualify in order for the whole phrase to qualify.  When
+** this routine is called, we know that pOrTerm did not qualify.
+** This routine merely checks to see if pOrTerm has a duplicate that
+** might qualify.  If there is a duplicate that has not yet been
+** disqualified, then return true.  If there are no duplicates, or
+** the duplicate has also been disqualifed, return false.
+*/
+static int orTermHasOkDuplicate(WhereClause *pOr, WhereTerm *pOrTerm){
+if( pOrTerm->flags & TERM_COPIED ){
+/* This is the original term.  The duplicate is to the left had
+** has not yet been analyzed and thus has not yet been disqualified. */
+return 1;
+}
+if( (pOrTerm->flags & TERM_VIRTUAL)!=0
+&& (pOr->a[pOrTerm->iParent].flags & TERM_OR_OK)!=0 ){
+/* This is a duplicate term.  The original qualified so this one
+** does not have to. */
+return 1;
+}
+/* This is either a singleton term or else it is a duplicate for
+** which the original did not qualify.  Either way we are done for. */
+return 0;
+}
+#endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */
+/*
+** The input to this routine is an WhereTerm structure with only the
+** "pExpr" field filled in.  The job of this routine is to analyze the
+** subexpression and populate all the other fields of the WhereTerm
+** structure.
+**
+** If the expression is of the form "<expr> <op> X" it gets commuted
+** to the standard form of "X <op> <expr>".  If the expression is of
+** the form "X <op> Y" where both X and Y are columns, then the original
+** expression is unchanged and a new virtual expression of the form
+** "Y <op> X" is added to the WHERE clause and analyzed separately.
+*/
+static void exprAnalyze(
+SrcList *pSrc,            /* the FROM clause */
+WhereClause *pWC,         /* the WHERE clause */
+int idxTerm               /* Index of the term to be analyzed */
+){
+WhereTerm *pTerm;
+ExprMaskSet *pMaskSet;
+Expr *pExpr;
+Bitmask prereqLeft;
+Bitmask prereqAll;
+int nPattern;
+int isComplete;
+int op;
+Parse *pParse = pWC->pParse;
+sqlite3 *db = pParse->db;
+if( db->mallocFailed ){
+return;
+}
+pTerm = &pWC->a[idxTerm];
+pMaskSet = pWC->pMaskSet;
+pExpr = pTerm->pExpr;
+prereqLeft = exprTableUsage(pMaskSet, pExpr->pLeft);
+op = pExpr->op;
+if( op==TK_IN ){
+assert( pExpr->pRight==0 );
+pTerm->prereqRight = exprListTableUsage(pMaskSet, pExpr->pList)
+| exprSelectTableUsage(pMaskSet, pExpr->pSelect);
+}else if( op==TK_ISNULL ){
+pTerm->prereqRight = 0;
+}else{
+pTerm->prereqRight = exprTableUsage(pMaskSet, pExpr->pRight);
+}
+prereqAll = exprTableUsage(pMaskSet, pExpr);
+if( ExprHasProperty(pExpr, EP_FromJoin) ){
+prereqAll |= getMask(pMaskSet, pExpr->iRightJoinTable);
+}
+pTerm->prereqAll = prereqAll;
+pTerm->leftCursor = -1;
+pTerm->iParent = -1;
+pTerm->eOperator = 0;
+if( allowedOp(op) && (pTerm->prereqRight & prereqLeft)==0 ){
+Expr *pLeft = pExpr->pLeft;
+Expr *pRight = pExpr->pRight;
+if( pLeft->op==TK_COLUMN ){
+pTerm->leftCursor = pLeft->iTable;
+pTerm->leftColumn = pLeft->iColumn;
+pTerm->eOperator = operatorMask(op);
+}
+if( pRight && pRight->op==TK_COLUMN ){
+WhereTerm *pNew;
+Expr *pDup;
+if( pTerm->leftCursor>=0 ){
+int idxNew;
+pDup = sqlite3ExprDup(db, pExpr);
+if( db->mallocFailed ){
+sqlite3ExprDelete(pDup);
+return;
+}
+idxNew = whereClauseInsert(pWC, pDup, TERM_VIRTUAL|TERM_DYNAMIC);
+if( idxNew==0 ) return;
+pNew = &pWC->a[idxNew];
+pNew->iParent = idxTerm;
+pTerm = &pWC->a[idxTerm];
+pTerm->nChild = 1;
+pTerm->flags |= TERM_COPIED;
+}else{
+pDup = pExpr;
+pNew = pTerm;
+}
+exprCommute(pDup);
+pLeft = pDup->pLeft;
+pNew->leftCursor = pLeft->iTable;
+pNew->leftColumn = pLeft->iColumn;
+pNew->prereqRight = prereqLeft;
+pNew->prereqAll = prereqAll;
+pNew->eOperator = operatorMask(pDup->op);
+}
+}
+#ifndef SQLITE_OMIT_BETWEEN_OPTIMIZATION
+/* If a term is the BETWEEN operator, create two new virtual terms
+** that define the range that the BETWEEN implements.
+*/
+else if( pExpr->op==TK_BETWEEN ){
+ExprList *pList = pExpr->pList;
+int i;
+static const u8 ops[] = {TK_GE, TK_LE};
+assert( pList!=0 );
+assert( pList->nExpr==2 );
+for(i=0; i<2; i++){
+Expr *pNewExpr;
+int idxNew;
+pNewExpr = sqlite3Expr(db, ops[i], sqlite3ExprDup(db, pExpr->pLeft),
+sqlite3ExprDup(db, pList->a[i].pExpr), 0);
+idxNew = whereClauseInsert(pWC, pNewExpr, TERM_VIRTUAL|TERM_DYNAMIC);
+exprAnalyze(pSrc, pWC, idxNew);
+pTerm = &pWC->a[idxTerm];
+pWC->a[idxNew].iParent = idxTerm;
+}
+pTerm->nChild = 2;
+}
+#endif /* SQLITE_OMIT_BETWEEN_OPTIMIZATION */
+#if !defined(SQLITE_OMIT_OR_OPTIMIZATION) && !defined(SQLITE_OMIT_SUBQUERY)
+/* Attempt to convert OR-connected terms into an IN operator so that
+** they can make use of indices.  Example:
+**
+**      x = expr1  OR  expr2 = x  OR  x = expr3
+**
+** is converted into
+**
+**      x IN (expr1,expr2,expr3)
+**
+** This optimization must be omitted if OMIT_SUBQUERY is defined because
+** the compiler for the the IN operator is part of sub-queries.
+*/
+else if( pExpr->op==TK_OR ){
+int ok;
+int i, j;
+int iColumn, iCursor;
+WhereClause sOr;
+WhereTerm *pOrTerm;
+assert( (pTerm->flags & TERM_DYNAMIC)==0 );
+whereClauseInit(&sOr, pWC->pParse, pMaskSet);
+whereSplit(&sOr, pExpr, TK_OR);
+exprAnalyzeAll(pSrc, &sOr);
+assert( sOr.nTerm>=2 );
+j = 0;
+do{
+assert( j<sOr.nTerm );
+iColumn = sOr.a[j].leftColumn;
+iCursor = sOr.a[j].leftCursor;
+ok = iCursor>=0;
+for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0 && ok; i--, pOrTerm++){
+if( pOrTerm->eOperator!=WO_EQ ){
+goto or_not_possible;
+}
+if( orTermIsOptCandidate(pOrTerm, iCursor, iColumn) ){
+pOrTerm->flags |= TERM_OR_OK;
+}else if( orTermHasOkDuplicate(&sOr, pOrTerm) ){
+pOrTerm->flags &= ~TERM_OR_OK;
+}else{
+ok = 0;
+}
+}
+}while( !ok && (sOr.a[j++].flags & TERM_COPIED)!=0 && j<2 );
+if( ok ){
+ExprList *pList = 0;
+Expr *pNew, *pDup;
+Expr *pLeft = 0;
+for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0 && ok; i--, pOrTerm++){
+if( (pOrTerm->flags & TERM_OR_OK)==0 ) continue;
+pDup = sqlite3ExprDup(db, pOrTerm->pExpr->pRight);
+pList = sqlite3ExprListAppend(pWC->pParse, pList, pDup, 0);
+pLeft = pOrTerm->pExpr->pLeft;
+}
+assert( pLeft!=0 );
+pDup = sqlite3ExprDup(db, pLeft);
+pNew = sqlite3Expr(db, TK_IN, pDup, 0, 0);
+if( pNew ){
+int idxNew;
+transferJoinMarkings(pNew, pExpr);
+pNew->pList = pList;
+idxNew = whereClauseInsert(pWC, pNew, TERM_VIRTUAL|TERM_DYNAMIC);
+exprAnalyze(pSrc, pWC, idxNew);
+pTerm = &pWC->a[idxTerm];
+pWC->a[idxNew].iParent = idxTerm;
+pTerm->nChild = 1;
+}else{
+sqlite3ExprListDelete(pList);
+}
+}
+or_not_possible:
+whereClauseClear(&sOr);
+}
+#endif /* SQLITE_OMIT_OR_OPTIMIZATION */
+#ifndef SQLITE_OMIT_LIKE_OPTIMIZATION
+/* Add constraints to reduce the search space on a LIKE or GLOB
+** operator.
+*/
+if( isLikeOrGlob(db, pExpr, &nPattern, &isComplete) ){
+Expr *pLeft, *pRight;
+Expr *pStr1, *pStr2;
+Expr *pNewExpr1, *pNewExpr2;
+int idxNew1, idxNew2;
+pLeft = pExpr->pList->a[1].pExpr;
+pRight = pExpr->pList->a[0].pExpr;
+pStr1 = sqlite3PExpr(pParse, TK_STRING, 0, 0, 0);
+if( pStr1 ){
+sqlite3TokenCopy(db, &pStr1->token, &pRight->token);
+pStr1->token.n = nPattern;
+pStr1->flags = EP_Dequoted;
+}
+pStr2 = sqlite3ExprDup(db, pStr1);
+if( !db->mallocFailed ){
+assert( pStr2->token.dyn );
+++*(u8*)&pStr2->token.z[nPattern-1];
+}
+pNewExpr1 = sqlite3PExpr(pParse, TK_GE, sqlite3ExprDup(db,pLeft), pStr1, 0);
+idxNew1 = whereClauseInsert(pWC, pNewExpr1, TERM_VIRTUAL|TERM_DYNAMIC);
+exprAnalyze(pSrc, pWC, idxNew1);
+pNewExpr2 = sqlite3PExpr(pParse, TK_LT, sqlite3ExprDup(db,pLeft), pStr2, 0);
+idxNew2 = whereClauseInsert(pWC, pNewExpr2, TERM_VIRTUAL|TERM_DYNAMIC);
+exprAnalyze(pSrc, pWC, idxNew2);
+pTerm = &pWC->a[idxTerm];
+if( isComplete ){
+pWC->a[idxNew1].iParent = idxTerm;
+pWC->a[idxNew2].iParent = idxTerm;
+pTerm->nChild = 2;
+}
+}
+#endif /* SQLITE_OMIT_LIKE_OPTIMIZATION */
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+/* Add a WO_MATCH auxiliary term to the constraint set if the
+** current expression is of the form:  column MATCH expr.
+** This information is used by the xBestIndex methods of
+** virtual tables.  The native query optimizer does not attempt
+** to do anything with MATCH functions.
+*/
+if( isMatchOfColumn(pExpr) ){
+int idxNew;
+Expr *pRight, *pLeft;
+WhereTerm *pNewTerm;
+Bitmask prereqColumn, prereqExpr;
+pRight = pExpr->pList->a[0].pExpr;
+pLeft = pExpr->pList->a[1].pExpr;
+prereqExpr = exprTableUsage(pMaskSet, pRight);
+prereqColumn = exprTableUsage(pMaskSet, pLeft);
+if( (prereqExpr & prereqColumn)==0 ){
+Expr *pNewExpr;
+pNewExpr = sqlite3Expr(db, TK_MATCH, 0, sqlite3ExprDup(db, pRight), 0);
+idxNew = whereClauseInsert(pWC, pNewExpr, TERM_VIRTUAL|TERM_DYNAMIC);
+pNewTerm = &pWC->a[idxNew];
+pNewTerm->prereqRight = prereqExpr;
+pNewTerm->leftCursor = pLeft->iTable;
+pNewTerm->leftColumn = pLeft->iColumn;
+pNewTerm->eOperator = WO_MATCH;
+pNewTerm->iParent = idxTerm;
+pTerm = &pWC->a[idxTerm];
+pTerm->nChild = 1;
+pTerm->flags |= TERM_COPIED;
+pNewTerm->prereqAll = pTerm->prereqAll;
+}
+}
+#endif /* SQLITE_OMIT_VIRTUALTABLE */
+}
+/*
+** Return TRUE if any of the expressions in pList->a[iFirst...] contain
+** a reference to any table other than the iBase table.
+*/
+static int referencesOtherTables(
+ExprList *pList,          /* Search expressions in ths list */
+ExprMaskSet *pMaskSet,    /* Mapping from tables to bitmaps */
+int iFirst,               /* Be searching with the iFirst-th expression */
+int iBase                 /* Ignore references to this table */
+){
+Bitmask allowed = ~getMask(pMaskSet, iBase);
+while( iFirst<pList->nExpr ){
+if( (exprTableUsage(pMaskSet, pList->a[iFirst++].pExpr)&allowed)!=0 ){
+return 1;
+}
+}
+return 0;
+}
+/*
+** This routine decides if pIdx can be used to satisfy the ORDER BY
+** clause.  If it can, it returns 1.  If pIdx cannot satisfy the
+** ORDER BY clause, this routine returns 0.
+**
+** pOrderBy is an ORDER BY clause from a SELECT statement.  pTab is the
+** left-most table in the FROM clause of that same SELECT statement and
+** the table has a cursor number of "base".  pIdx is an index on pTab.
+**
+** nEqCol is the number of columns of pIdx that are used as equality
+** constraints.  Any of these columns may be missing from the ORDER BY
+** clause and the match can still be a success.
+**
+** All terms of the ORDER BY that match against the index must be either
+** ASC or DESC.  (Terms of the ORDER BY clause past the end of a UNIQUE
+** index do not need to satisfy this constraint.)  The *pbRev value is
+** set to 1 if the ORDER BY clause is all DESC and it is set to 0 if
+** the ORDER BY clause is all ASC.
+*/
+static int isSortingIndex(
+Parse *pParse,          /* Parsing context */
+ExprMaskSet *pMaskSet,  /* Mapping from table indices to bitmaps */
+Index *pIdx,            /* The index we are testing */
+int base,               /* Cursor number for the table to be sorted */
+ExprList *pOrderBy,     /* The ORDER BY clause */
+int nEqCol,             /* Number of index columns with == constraints */
+int *pbRev              /* Set to 1 if ORDER BY is DESC */
+){
+int i, j;                       /* Loop counters */
+int sortOrder = 0;              /* XOR of index and ORDER BY sort direction */
+int nTerm;                      /* Number of ORDER BY terms */
+ExprList::ExprList_item *pTerm;    /* A term of the ORDER BY clause */
+sqlite3 *db = pParse->db;
+assert( pOrderBy!=0 );
+nTerm = pOrderBy->nExpr;
+assert( nTerm>0 );
+/* Match terms of the ORDER BY clause against columns of
+** the index.
+**
+** Note that indices have pIdx->nColumn regular columns plus
+** one additional column containing the rowid.  The rowid column
+** of the index is also allowed to match against the ORDER BY
+** clause.
+*/
+for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<=pIdx->nColumn; i++){
+Expr *pExpr;       /* The expression of the ORDER BY pTerm */
+CollSeq *pColl;    /* The collating sequence of pExpr */
+int termSortOrder; /* Sort order for this term */
+int iColumn;       /* The i-th column of the index.  -1 for rowid */
+int iSortOrder;    /* 1 for DESC, 0 for ASC on the i-th index term */
+const char *zColl; /* Name of the collating sequence for i-th index term */
+pExpr = pTerm->pExpr;
+if( pExpr->op!=TK_COLUMN || pExpr->iTable!=base ){
+/* Can not use an index sort on anything that is not a column in the
+** left-most table of the FROM clause */
+break;
+}
+pColl = sqlite3ExprCollSeq(pParse, pExpr);
+if( !pColl ){
+pColl = db->pDfltColl;
+}
+if( i<pIdx->nColumn ){
+iColumn = pIdx->aiColumn[i];
+if( iColumn==pIdx->pTable->iPKey ){
+iColumn = -1;
+}
+iSortOrder = pIdx->aSortOrder[i];
+zColl = pIdx->azColl[i];
+}else{
+iColumn = -1;
+iSortOrder = 0;
+zColl = pColl->zName;
+}
+if( pExpr->iColumn!=iColumn || sqlite3StrICmp(pColl->zName, zColl) ){
+/* Term j of the ORDER BY clause does not match column i of the index */
+if( i<nEqCol ){
+/* If an index column that is constrained by == fails to match an
+** ORDER BY term, that is OK.  Just ignore that column of the index
+*/
+continue;
+}else{
+/* If an index column fails to match and is not constrained by ==
+** then the index cannot satisfy the ORDER BY constraint.
+*/
+return 0;
+}
+}
+assert( pIdx->aSortOrder!=0 );
+assert( pTerm->sortOrder==0 || pTerm->sortOrder==1 );
+assert( iSortOrder==0 || iSortOrder==1 );
+termSortOrder = iSortOrder ^ pTerm->sortOrder;
+if( i>nEqCol ){
+if( termSortOrder!=sortOrder ){
+/* Indices can only be used if all ORDER BY terms past the
+** equality constraints are all either DESC or ASC. */
+return 0;
+}
+}else{
+sortOrder = termSortOrder;
+}
+j++;
+pTerm++;
+if( iColumn<0 && !referencesOtherTables(pOrderBy, pMaskSet, j, base) ){
+/* If the indexed column is the primary key and everything matches
+** so far and none of the ORDER BY terms to the right reference other
+** tables in the join, then we are assured that the index can be used
+** to sort because the primary key is unique and so none of the other
+** columns will make any difference
+*/
+j = nTerm;
+}
+}
+*pbRev = sortOrder!=0;
+if( j>=nTerm ){
+/* All terms of the ORDER BY clause are covered by this index so
+** this index can be used for sorting. */
+return 1;
+}
+if( pIdx->onError!=OE_None && i==pIdx->nColumn
+&& !referencesOtherTables(pOrderBy, pMaskSet, j, base) ){
+/* All terms of this index match some prefix of the ORDER BY clause
+** and the index is UNIQUE and no terms on the tail of the ORDER BY
+** clause reference other tables in a join.  If this is all true then
+** the order by clause is superfluous. */
+return 1;
+}
+return 0;
+}
+/*
+** Check table to see if the ORDER BY clause in pOrderBy can be satisfied
+** by sorting in order of ROWID.  Return true if so and set *pbRev to be
+** true for reverse ROWID and false for forward ROWID order.
+*/
+static int sortableByRowid(
+int base,               /* Cursor number for table to be sorted */
+ExprList *pOrderBy,     /* The ORDER BY clause */
+ExprMaskSet *pMaskSet,  /* Mapping from tables to bitmaps */
+int *pbRev              /* Set to 1 if ORDER BY is DESC */
+){
+Expr *p;
+assert( pOrderBy!=0 );
+assert( pOrderBy->nExpr>0 );
+p = pOrderBy->a[0].pExpr;
+if( p->op==TK_COLUMN && p->iTable==base && p->iColumn==-1
+&& !referencesOtherTables(pOrderBy, pMaskSet, 1, base) ){
+*pbRev = pOrderBy->a[0].sortOrder;
+return 1;
+}
+return 0;
+}
+/*
+** Prepare a crude estimate of the logarithm of the input value.
+** The results need not be exact.  This is only used for estimating
+** the total cost of performing operatings with O(logN) or O(NlogN)
+** complexity.  Because N is just a guess, it is no great tragedy if
+** logN is a little off.
+*/
+static double estLog(double N){
+double logN = 1;
+double x = 10;
+while( N>x ){
+logN += 1;
+x *= 10;
+}
+return logN;
+}
+/*
+** Two routines for printing the content of an sqlite3_index_info
+** structure.  Used for testing and debugging only.  If neither
+** SQLITE_TEST or SQLITE_DEBUG are defined, then these routines
+** are no-ops.
+*/
+#if !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_DEBUG)
+static void TRACE_IDX_INPUTS(sqlite3_index_info *p){
+int i;
+if( !sqlite3_where_trace ) return;
+for(i=0; i<p->nConstraint; i++){
+sqlite3DebugPrintf("  constraint[%d]: col=%d termid=%d op=%d usabled=%d\n",
+i,
+p->aConstraint[i].iColumn,
+p->aConstraint[i].iTermOffset,
+p->aConstraint[i].op,
+p->aConstraint[i].usable);
+}
+for(i=0; i<p->nOrderBy; i++){
+sqlite3DebugPrintf("  orderby[%d]: col=%d desc=%d\n",
+i,
+p->aOrderBy[i].iColumn,
+p->aOrderBy[i].desc);
+}
+}
+static void TRACE_IDX_OUTPUTS(sqlite3_index_info *p){
+int i;
+if( !sqlite3_where_trace ) return;
+for(i=0; i<p->nConstraint; i++){
+sqlite3DebugPrintf("  usage[%d]: argvIdx=%d omit=%d\n",
+i,
+p->aConstraintUsage[i].argvIndex,
+p->aConstraintUsage[i].omit);
+}
+sqlite3DebugPrintf("  idxNum=%d\n", p->idxNum);
+sqlite3DebugPrintf("  idxStr=%s\n", p->idxStr);
+sqlite3DebugPrintf("  orderByConsumed=%d\n", p->orderByConsumed);
+sqlite3DebugPrintf("  estimatedCost=%g\n", p->estimatedCost);
+}
+#else
+#define TRACE_IDX_INPUTS(A)
+#define TRACE_IDX_OUTPUTS(A)
+#endif
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+/*
+** Compute the best index for a virtual table.
+**
+** The best index is computed by the xBestIndex method of the virtual
+** table module.  This routine is really just a wrapper that sets up
+** the sqlite3_index_info structure that is used to communicate with
+** xBestIndex.
+**
+** In a join, this routine might be called multiple times for the
+** same virtual table.  The sqlite3_index_info structure is created
+** and initialized on the first invocation and reused on all subsequent
+** invocations.  The sqlite3_index_info structure is also used when
+** code is generated to access the virtual table.  The whereInfoDelete()
+** routine takes care of freeing the sqlite3_index_info structure after
+** everybody has finished with it.
+*/
+static double bestVirtualIndex(
+Parse *pParse,                 /* The parsing context */
+WhereClause *pWC,              /* The WHERE clause */
+SrcList::SrcList_item *pSrc,     /* The FROM clause term to search */
+Bitmask notReady,              /* Mask of cursors that are not available */
+ExprList *pOrderBy,            /* The order by clause */
+int orderByUsable,             /* True if we can potential sort */
+sqlite3_index_info **ppIdxInfo /* Index information passed to xBestIndex */
+){
+Table *pTab = pSrc->pTab;
+sqlite3_index_info *pIdxInfo;
+sqlite3_index_info::sqlite3_index_constraint *pIdxCons;
+sqlite3_index_info::sqlite3_index_orderby *pIdxOrderBy;
+sqlite3_index_info::sqlite3_index_constraint_usage *pUsage;
+WhereTerm *pTerm;
+int i, j;
+int nOrderBy;
+int rc;
+/* If the sqlite3_index_info structure has not been previously
+** allocated and initialized for this virtual table, then allocate
+** and initialize it now
+*/
+pIdxInfo = *ppIdxInfo;
+if( pIdxInfo==0 ){
+WhereTerm *pTerm;
+int nTerm;
+WHERETRACE(("Recomputing index info for %s...\n", pTab->zName));
+/* Count the number of possible WHERE clause constraints referring
+** to this virtual table */
+for(i=nTerm=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
+if( pTerm->leftCursor != pSrc->iCursor ) continue;
+if( pTerm->eOperator==WO_IN ) continue;
+if( pTerm->eOperator==WO_ISNULL ) continue;
+nTerm++;
+}
+/* If the ORDER BY clause contains only columns in the current
+** virtual table then allocate space for the aOrderBy part of
+** the sqlite3_index_info structure.
+*/
+nOrderBy = 0;
+if( pOrderBy ){
+for(i=0; i<pOrderBy->nExpr; i++){
+Expr *pExpr = pOrderBy->a[i].pExpr;
+if( pExpr->op!=TK_COLUMN || pExpr->iTable!=pSrc->iCursor ) break;
+}
+if( i==pOrderBy->nExpr ){
+nOrderBy = pOrderBy->nExpr;
+}
+}
+/* Allocate the sqlite3_index_info structure
+*/
+pIdxInfo = (sqlite3_index_info*)sqlite3DbMallocZero(pParse->db, sizeof(*pIdxInfo)
++ (sizeof(*pIdxCons) + sizeof(*pUsage))*nTerm
++ sizeof(*pIdxOrderBy)*nOrderBy );
+if( pIdxInfo==0 ){
+sqlite3ErrorMsg(pParse, "out of memory");
+return 0.0;
+}
+*ppIdxInfo = pIdxInfo;
+/* Initialize the structure.  The sqlite3_index_info structure contains
+** many fields that are declared "const" to prevent xBestIndex from
+** changing them.  We have to do some funky casting in order to
+** initialize those fields.
+*/
+	pIdxCons = (sqlite3_index_info::sqlite3_index_constraint*)&pIdxInfo[1];
+	pIdxOrderBy = (sqlite3_index_info::sqlite3_index_orderby*)&pIdxCons[nTerm];
+	pUsage = (sqlite3_index_info::sqlite3_index_constraint_usage*)&pIdxOrderBy[nOrderBy];
+*(int*)&pIdxInfo->nConstraint = nTerm;
+*(int*)&pIdxInfo->nOrderBy = nOrderBy;
+	*(sqlite3_index_info::sqlite3_index_constraint**)&pIdxInfo->aConstraint = pIdxCons;
+	*(sqlite3_index_info::sqlite3_index_orderby**)&pIdxInfo->aOrderBy = pIdxOrderBy;
+	*(sqlite3_index_info::sqlite3_index_constraint_usage**)&pIdxInfo->aConstraintUsage =
+pUsage;
+for(i=j=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
+if( pTerm->leftCursor != pSrc->iCursor ) continue;
+if( pTerm->eOperator==WO_IN ) continue;
+if( pTerm->eOperator==WO_ISNULL ) continue;
+pIdxCons[j].iColumn = pTerm->leftColumn;
+pIdxCons[j].iTermOffset = i;
+pIdxCons[j].op = pTerm->eOperator;
+/* The direct assignment in the previous line is possible only because
+** the WO_ and SQLITE_INDEX_CONSTRAINT_ codes are identical.  The
+** following asserts verify this fact. */
+assert( WO_EQ==SQLITE_INDEX_CONSTRAINT_EQ );
+assert( WO_LT==SQLITE_INDEX_CONSTRAINT_LT );
+assert( WO_LE==SQLITE_INDEX_CONSTRAINT_LE );
+assert( WO_GT==SQLITE_INDEX_CONSTRAINT_GT );
+assert( WO_GE==SQLITE_INDEX_CONSTRAINT_GE );
+assert( WO_MATCH==SQLITE_INDEX_CONSTRAINT_MATCH );
+assert( pTerm->eOperator & (WO_EQ|WO_LT|WO_LE|WO_GT|WO_GE|WO_MATCH) );
+j++;
+}
+for(i=0; i<nOrderBy; i++){
+Expr *pExpr = pOrderBy->a[i].pExpr;
+pIdxOrderBy[i].iColumn = pExpr->iColumn;
+pIdxOrderBy[i].desc = pOrderBy->a[i].sortOrder;
+}
+}
+/* At this point, the sqlite3_index_info structure that pIdxInfo points
+** to will have been initialized, either during the current invocation or
+** during some prior invocation.  Now we just have to customize the
+** details of pIdxInfo for the current invocation and pass it to
+** xBestIndex.
+*/
+/* The module name must be defined. Also, by this point there must
+** be a pointer to an sqlite3_vtab structure. Otherwise
+** sqlite3ViewGetColumnNames() would have picked up the error.
+*/
+assert( pTab->azModuleArg && pTab->azModuleArg[0] );
+assert( pTab->pVtab );
+#if 0
+if( pTab->pVtab==0 ){
+sqlite3ErrorMsg(pParse, "undefined module %s for table %s",
+pTab->azModuleArg[0], pTab->zName);
+return 0.0;
+}
+#endif
+/* Set the aConstraint[].usable fields and initialize all
+** output variables to zero.
+**
+** aConstraint[].usable is true for constraints where the right-hand
+** side contains only references to tables to the left of the current
+** table.  In other words, if the constraint is of the form:
+**
+**           column = expr
+**
+** and we are evaluating a join, then the constraint on column is
+** only valid if all tables referenced in expr occur to the left
+** of the table containing column.
+**
+** The aConstraints[] array contains entries for all constraints
+** on the current table.  That way we only have to compute it once
+** even though we might try to pick the best index multiple times.
+** For each attempt at picking an index, the order of tables in the
+** join might be different so we have to recompute the usable flag
+** each time.
+*/
+pIdxCons = *(sqlite3_index_info::sqlite3_index_constraint**)&pIdxInfo->aConstraint;
+pUsage = pIdxInfo->aConstraintUsage;
+for(i=0; i<pIdxInfo->nConstraint; i++, pIdxCons++){
+j = pIdxCons->iTermOffset;
+pTerm = &pWC->a[j];
+pIdxCons->usable =  (pTerm->prereqRight & notReady)==0;
+}
+memset(pUsage, 0, sizeof(pUsage[0])*pIdxInfo->nConstraint);
+if( pIdxInfo->needToFreeIdxStr ){
+sqlite3_free(pIdxInfo->idxStr);
+}
+pIdxInfo->idxStr = 0;
+pIdxInfo->idxNum = 0;
+pIdxInfo->needToFreeIdxStr = 0;
+pIdxInfo->orderByConsumed = 0;
+pIdxInfo->estimatedCost = SQLITE_BIG_DBL / 2.0;
+nOrderBy = pIdxInfo->nOrderBy;
+if( pIdxInfo->nOrderBy && !orderByUsable ){
+*(int*)&pIdxInfo->nOrderBy = 0;
+}
+sqlite3SafetyOff(pParse->db);
+WHERETRACE(("xBestIndex for %s\n", pTab->zName));
+TRACE_IDX_INPUTS(pIdxInfo);
+rc = pTab->pVtab->pModule->xBestIndex(pTab->pVtab, pIdxInfo);
+TRACE_IDX_OUTPUTS(pIdxInfo);
+if( rc!=SQLITE_OK ){
+if( rc==SQLITE_NOMEM ){
+pParse->db->mallocFailed = 1;
+}else {
+sqlite3ErrorMsg(pParse, "%s", sqlite3ErrStr(rc));
+}
+sqlite3SafetyOn(pParse->db);
+}else{
+rc = sqlite3SafetyOn(pParse->db);
+}
+*(int*)&pIdxInfo->nOrderBy = nOrderBy;
+return pIdxInfo->estimatedCost;
+}
+#endif /* SQLITE_OMIT_VIRTUALTABLE */
+/*
+** Find the best index for accessing a particular table.  Return a pointer
+** to the index, flags that describe how the index should be used, the
+** number of equality constraints, and the "cost" for this index.
+**
+** The lowest cost index wins.  The cost is an estimate of the amount of
+** CPU and disk I/O need to process the request using the selected index.
+** Factors that influence cost include:
+**
+**    *  The estimated number of rows that will be retrieved.  (The
+**       fewer the better.)
+**
+**    *  Whether or not sorting must occur.
+**
+**    *  Whether or not there must be separate lookups in the
+**       index and in the main table.
+**
+*/
+static double bestIndex(
+Parse *pParse,              /* The parsing context */
+WhereClause *pWC,           /* The WHERE clause */
+SrcList::SrcList_item *pSrc,  /* The FROM clause term to search */
+Bitmask notReady,           /* Mask of cursors that are not available */
+ExprList *pOrderBy,         /* The order by clause */
+Index **ppIndex,            /* Make *ppIndex point to the best index */
+int *pFlags,                /* Put flags describing this choice in *pFlags */
+int *pnEq                   /* Put the number of == or IN constraints here */
+){
+WhereTerm *pTerm;
+Index *bestIdx = 0;         /* Index that gives the lowest cost */
+double lowestCost;          /* The cost of using bestIdx */
+int bestFlags = 0;          /* Flags associated with bestIdx */
+int bestNEq = 0;            /* Best value for nEq */
+int iCur = pSrc->iCursor;   /* The cursor of the table to be accessed */
+Index *pProbe;              /* An index we are evaluating */
+int rev;                    /* True to scan in reverse order */
+int flags;                  /* Flags associated with pProbe */
+int nEq;                    /* Number of == or IN constraints */
+int eqTermMask;             /* Mask of valid equality operators */
+double cost;                /* Cost of using pProbe */
+WHERETRACE(("bestIndex: tbl=%s notReady=%x\n", pSrc->pTab->zName, notReady));
+lowestCost = SQLITE_BIG_DBL;
+pProbe = pSrc->pTab->pIndex;
+/* If the table has no indices and there are no terms in the where
+** clause that refer to the ROWID, then we will never be able to do
+** anything other than a full table scan on this table.  We might as
+** well put it first in the join order.  That way, perhaps it can be
+** referenced by other tables in the join.
+*/
+if( pProbe==0 &&
+findTerm(pWC, iCur, -1, 0, WO_EQ|WO_IN|WO_LT|WO_LE|WO_GT|WO_GE,0)==0 &&
+(pOrderBy==0 || !sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev)) ){
+*pFlags = 0;
+*ppIndex = 0;
+*pnEq = 0;
+return 0.0;
+}
+/* Check for a rowid=EXPR or rowid IN (...) constraints
+*/
+pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);
+if( pTerm ){
+Expr *pExpr;
+*ppIndex = 0;
+bestFlags = WHERE_ROWID_EQ;
+if( pTerm->eOperator & WO_EQ ){
+/* Rowid== is always the best pick.  Look no further.  Because only
+** a single row is generated, output is always in sorted order */
+*pFlags = WHERE_ROWID_EQ | WHERE_UNIQUE;
+*pnEq = 1;
+WHERETRACE(("... best is rowid\n"));
+return 0.0;
+}else if( (pExpr = pTerm->pExpr)->pList!=0 ){
+/* Rowid IN (LIST): cost is NlogN where N is the number of list
+** elements.  */
+lowestCost = pExpr->pList->nExpr;
+lowestCost *= estLog(lowestCost);
+}else{
+/* Rowid IN (SELECT): cost is NlogN where N is the number of rows
+** in the result of the inner select.  We have no way to estimate
+** that value so make a wild guess. */
+lowestCost = 200;
+}
+WHERETRACE(("... rowid IN cost: %.9g\n", lowestCost));
+}
+/* Estimate the cost of a table scan.  If we do not know how many
+** entries are in the table, use 1 million as a guess.
+*/
+cost = pProbe ? pProbe->aiRowEst[0] : 1000000;
+WHERETRACE(("... table scan base cost: %.9g\n", cost));
+flags = WHERE_ROWID_RANGE;
+/* Check for constraints on a range of rowids in a table scan.
+*/
+pTerm = findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE|WO_GT|WO_GE, 0);
+if( pTerm ){
+if( findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE, 0) ){
+flags |= WHERE_TOP_LIMIT;
+cost /= 3;  /* Guess that rowid<EXPR eliminates two-thirds or rows */
+}
+if( findTerm(pWC, iCur, -1, notReady, WO_GT|WO_GE, 0) ){
+flags |= WHERE_BTM_LIMIT;
+cost /= 3;  /* Guess that rowid>EXPR eliminates two-thirds of rows */
+}
+WHERETRACE(("... rowid range reduces cost to %.9g\n", cost));
+}else{
+flags = 0;
+}
+/* If the table scan does not satisfy the ORDER BY clause, increase
+** the cost by NlogN to cover the expense of sorting. */
+if( pOrderBy ){
+if( sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev) ){
+flags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;
+if( rev ){
+flags |= WHERE_REVERSE;
+}
+}else{
+cost += cost*estLog(cost);
+WHERETRACE(("... sorting increases cost to %.9g\n", cost));
+}
+}
+if( cost<lowestCost ){
+lowestCost = cost;
+bestFlags = flags;
+}
+/* If the pSrc table is the right table of a LEFT JOIN then we may not
+** use an index to satisfy IS NULL constraints on that table.  This is
+** because columns might end up being NULL if the table does not match -
+** a circumstance which the index cannot help us discover.  Ticket #2177.
+*/
+if( (pSrc->jointype & JT_LEFT)!=0 ){
+eqTermMask = WO_EQ|WO_IN;
+}else{
+eqTermMask = WO_EQ|WO_IN|WO_ISNULL;
+}
+/* Look at each index.
+*/
+for(; pProbe; pProbe=pProbe->pNext){
+int i;                       /* Loop counter */
+double inMultiplier = 1;
+WHERETRACE(("... index %s:\n", pProbe->zName));
+/* Count the number of columns in the index that are satisfied
+** by x=EXPR constraints or x IN (...) constraints.
+*/
+flags = 0;
+for(i=0; i<pProbe->nColumn; i++){
+int j = pProbe->aiColumn[i];
+pTerm = findTerm(pWC, iCur, j, notReady, eqTermMask, pProbe);
+if( pTerm==0 ) break;
+flags |= WHERE_COLUMN_EQ;
+if( pTerm->eOperator & WO_IN ){
+Expr *pExpr = pTerm->pExpr;
+flags |= WHERE_COLUMN_IN;
+if( pExpr->pSelect!=0 ){
+inMultiplier *= 25;
+}else if( pExpr->pList!=0 ){
+inMultiplier *= pExpr->pList->nExpr + 1;
+}
+}
+}
+cost = pProbe->aiRowEst[i] * inMultiplier * estLog(inMultiplier);
+nEq = i;
+if( pProbe->onError!=OE_None && (flags & WHERE_COLUMN_IN)==0
+&& nEq==pProbe->nColumn ){
+flags |= WHERE_UNIQUE;
+}
+WHERETRACE(("...... nEq=%d inMult=%.9g cost=%.9g\n",nEq,inMultiplier,cost));
+/* Look for range constraints
+*/
+if( nEq<pProbe->nColumn ){
+int j = pProbe->aiColumn[nEq];
+pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);
+if( pTerm ){
+flags |= WHERE_COLUMN_RANGE;
+if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pProbe) ){
+flags |= WHERE_TOP_LIMIT;
+cost /= 3;
+}
+if( findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pProbe) ){
+flags |= WHERE_BTM_LIMIT;
+cost /= 3;
+}
+WHERETRACE(("...... range reduces cost to %.9g\n", cost));
+}
+}
+/* Add the additional cost of sorting if that is a factor.
+*/
+if( pOrderBy ){
+if( (flags & WHERE_COLUMN_IN)==0 &&
+isSortingIndex(pParse,pWC->pMaskSet,pProbe,iCur,pOrderBy,nEq,&rev) ){
+if( flags==0 ){
+flags = WHERE_COLUMN_RANGE;
+}
+flags |= WHERE_ORDERBY;
+if( rev ){
+flags |= WHERE_REVERSE;
+}
+}else{
+cost += cost*estLog(cost);
+WHERETRACE(("...... orderby increases cost to %.9g\n", cost));
+}
+}
+/* Check to see if we can get away with using just the index without
+** ever reading the table.  If that is the case, then halve the
+** cost of this index.
+*/
+if( flags && pSrc->colUsed < (((Bitmask)1)<<(BMS-1)) ){
+Bitmask m = pSrc->colUsed;
+int j;
+for(j=0; j<pProbe->nColumn; j++){
+int x = pProbe->aiColumn[j];
+if( x<BMS-1 ){
+m &= ~(((Bitmask)1)<<x);
+}
+}
+if( m==0 ){
+flags |= WHERE_IDX_ONLY;
+cost /= 2;
+WHERETRACE(("...... idx-only reduces cost to %.9g\n", cost));
+}
+}
+/* If this index has achieved the lowest cost so far, then use it.
+*/
+if( flags && cost < lowestCost ){
+bestIdx = pProbe;
+lowestCost = cost;
+bestFlags = flags;
+bestNEq = nEq;
+}
+}
+/* Report the best result
+*/
+*ppIndex = bestIdx;
+WHERETRACE(("best index is %s, cost=%.9g, flags=%x, nEq=%d\n",
+bestIdx ? bestIdx->zName : "(none)", lowestCost, bestFlags, bestNEq));
+*pFlags = bestFlags | eqTermMask;
+*pnEq = bestNEq;
+return lowestCost;
+}
+/*
+** Disable a term in the WHERE clause.  Except, do not disable the term
+** if it controls a LEFT OUTER JOIN and it did not originate in the ON
+** or USING clause of that join.
+**
+** Consider the term t2.z='ok' in the following queries:
+**
+**   (1)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x WHERE t2.z='ok'
+**   (2)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x AND t2.z='ok'
+**   (3)  SELECT * FROM t1, t2 WHERE t1.a=t2.x AND t2.z='ok'
+**
+** The t2.z='ok' is disabled in the in (2) because it originates
+** in the ON clause.  The term is disabled in (3) because it is not part
+** of a LEFT OUTER JOIN.  In (1), the term is not disabled.
+**
+** Disabling a term causes that term to not be tested in the inner loop
+** of the join.  Disabling is an optimization.  When terms are satisfied
+** by indices, we disable them to prevent redundant tests in the inner
+** loop.  We would get the correct results if nothing were ever disabled,
+** but joins might run a little slower.  The trick is to disable as much
+** as we can without disabling too much.  If we disabled in (1), we'd get
+** the wrong answer.  See ticket #813.
+*/
+static void disableTerm(WhereLevel *pLevel, WhereTerm *pTerm){
+if( pTerm
+&& (pTerm->flags & TERM_CODED)==0
+&& (pLevel->iLeftJoin==0 || ExprHasProperty(pTerm->pExpr, EP_FromJoin))
+){
+pTerm->flags |= TERM_CODED;
+if( pTerm->iParent>=0 ){
+WhereTerm *pOther = &pTerm->pWC->a[pTerm->iParent];
+if( (--pOther->nChild)==0 ){
+disableTerm(pLevel, pOther);
+}
+}
+}
+}
+/*
+** Generate code that builds a probe for an index.
+**
+** There should be nColumn values on the stack.  The index
+** to be probed is pIdx.  Pop the values from the stack and
+** replace them all with a single record that is the index
+** problem.
+*/
+static void buildIndexProbe(
+Vdbe *v,        /* Generate code into this VM */
+int nColumn,    /* The number of columns to check for NULL */
+Index *pIdx     /* Index that we will be searching */
+){
+sqlite3VdbeAddOp(v, OP_MakeRecord, nColumn, 0);
+sqlite3IndexAffinityStr(v, pIdx);
+}
+/*
+** Generate code for a single equality term of the WHERE clause.  An equality
+** term can be either X=expr or X IN (...).   pTerm is the term to be
+** coded.
+**
+** The current value for the constraint is left on the top of the stack.
+**
+** For a constraint of the form X=expr, the expression is evaluated and its
+** result is left on the stack.  For constraints of the form X IN (...)
+** this routine sets up a loop that will iterate over all values of X.
+*/
+static void codeEqualityTerm(
+Parse *pParse,      /* The parsing context */
+WhereTerm *pTerm,   /* The term of the WHERE clause to be coded */
+WhereLevel *pLevel  /* When level of the FROM clause we are working on */
+){
+Expr *pX = pTerm->pExpr;
+Vdbe *v = pParse->pVdbe;
+if( pX->op==TK_EQ ){
+sqlite3ExprCode(pParse, pX->pRight);
+}else if( pX->op==TK_ISNULL ){
+sqlite3VdbeAddOp(v, OP_Null, 0, 0);
+#ifndef SQLITE_OMIT_SUBQUERY
+}else{
+int eType;
+int iTab;
+	WhereLevel::InLoop *pIn;
+assert( pX->op==TK_IN );
+eType = sqlite3FindInIndex(pParse, pX, 1);
+iTab = pX->iTable;
+sqlite3VdbeAddOp(v, OP_Rewind, iTab, 0);
+VdbeComment((v, "# %.*s", pX->span.n, pX->span.z));
+if( pLevel->nIn==0 ){
+pLevel->nxt = sqlite3VdbeMakeLabel(v);
+}
+pLevel->nIn++;
+	pLevel->aInLoop = (WhereLevel::InLoop*)sqlite3DbReallocOrFree(pParse->db, pLevel->aInLoop,
+sizeof(pLevel->aInLoop[0])*pLevel->nIn);
+	pIn = (WhereLevel::InLoop*)pLevel->aInLoop;
+if( pIn ){
+int op = ((eType==IN_INDEX_ROWID)?OP_Rowid:OP_Column);
+pIn += pLevel->nIn - 1;
+pIn->iCur = iTab;
+pIn->topAddr = sqlite3VdbeAddOp(v, op, iTab, 0);
+sqlite3VdbeAddOp(v, OP_IsNull, -1, 0);
+}else{
+pLevel->nIn = 0;
+}
+#endif
+}
+disableTerm(pLevel, pTerm);
+}
+/*
+** Generate code that will evaluate all == and IN constraints for an
+** index.  The values for all constraints are left on the stack.
+**
+** For example, consider table t1(a,b,c,d,e,f) with index i1(a,b,c).
+** Suppose the WHERE clause is this:  a==5 AND b IN (1,2,3) AND c>5 AND c<10
+** The index has as many as three equality constraints, but in this
+** example, the third "c" value is an inequality.  So only two
+** constraints are coded.  This routine will generate code to evaluate
+** a==5 and b IN (1,2,3).  The current values for a and b will be left
+** on the stack - a is the deepest and b the shallowest.
+**
+** In the example above nEq==2.  But this subroutine works for any value
+** of nEq including 0.  If nEq==0, this routine is nearly a no-op.
+** The only thing it does is allocate the pLevel->iMem memory cell.
+**
+** This routine always allocates at least one memory cell and puts
+** the address of that memory cell in pLevel->iMem.  The code that
+** calls this routine will use pLevel->iMem to store the termination
+** key value of the loop.  If one or more IN operators appear, then
+** this routine allocates an additional nEq memory cells for internal
+** use.
+*/
+static void codeAllEqualityTerms(
+Parse *pParse,        /* Parsing context */
+WhereLevel *pLevel,   /* Which nested loop of the FROM we are coding */
+WhereClause *pWC,     /* The WHERE clause */
+Bitmask notReady      /* Which parts of FROM have not yet been coded */
+){
+int nEq = pLevel->nEq;        /* The number of == or IN constraints to code */
+int termsInMem = 0;           /* If true, store value in mem[] cells */
+Vdbe *v = pParse->pVdbe;      /* The virtual machine under construction */
+Index *pIdx = pLevel->pIdx;   /* The index being used for this loop */
+int iCur = pLevel->iTabCur;   /* The cursor of the table */
+WhereTerm *pTerm;             /* A single constraint term */
+int j;                        /* Loop counter */
+/* Figure out how many memory cells we will need then allocate them.
+** We always need at least one used to store the loop terminator
+** value.  If there are IN operators we'll need one for each == or
+** IN constraint.
+*/
+pLevel->iMem = pParse->nMem++;
+if( pLevel->flags & WHERE_COLUMN_IN ){
+pParse->nMem += pLevel->nEq;
+termsInMem = 1;
+}
+/* Evaluate the equality constraints
+*/
+assert( pIdx->nColumn>=nEq );
+for(j=0; j<nEq; j++){
+int k = pIdx->aiColumn[j];
+pTerm = findTerm(pWC, iCur, k, notReady, pLevel->flags, pIdx);
+if( pTerm==0 ) break;
+assert( (pTerm->flags & TERM_CODED)==0 );
+codeEqualityTerm(pParse, pTerm, pLevel);
+if( (pTerm->eOperator & (WO_ISNULL|WO_IN))==0 ){
+sqlite3VdbeAddOp(v, OP_IsNull, termsInMem ? -1 : -(j+1), pLevel->brk);
+}
+if( termsInMem ){
+sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem+j+1, 1);
+}
+}
+/* Make sure all the constraint values are on the top of the stack
+*/
+if( termsInMem ){
+for(j=0; j<nEq; j++){
+sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem+j+1, 0);
+}
+}
+}
+#if defined(SQLITE_TEST)
+/*
+** The following variable holds a text description of query plan generated
+** by the most recent call to sqlite3WhereBegin().  Each call to WhereBegin
+** overwrites the previous.  This information is used for testing and
+** analysis only.
+*/
+char sqlite3_query_plan[BMS*2*40];  /* Text of the join */
+static int nQPlan = 0;              /* Next free slow in _query_plan[] */
+#endif /* SQLITE_TEST */
+/*
+** Free a WhereInfo structure
+*/
+static void whereInfoFree(WhereInfo *pWInfo){
+if( pWInfo ){
+int i;
+for(i=0; i<pWInfo->nLevel; i++){
+sqlite3_index_info *pInfo = pWInfo->a[i].pIdxInfo;
+if( pInfo ){
+if( pInfo->needToFreeIdxStr ){
+/* Coverage: Don't think this can be reached. By the time this
+** function is called, the index-strings have been passed
+** to the vdbe layer for deletion.
+*/
+sqlite3_free(pInfo->idxStr);
+}
+sqlite3_free(pInfo);
+}
+}
+sqlite3_free(pWInfo);
+}
+}
+/*
+** Generate the beginning of the loop used for WHERE clause processing.
+** The return value is a pointer to an opaque structure that contains
+** information needed to terminate the loop.  Later, the calling routine
+** should invoke sqlite3WhereEnd() with the return value of this function
+** in order to complete the WHERE clause processing.
+**
+** If an error occurs, this routine returns NULL.
+**
+** The basic idea is to do a nested loop, one loop for each table in
+** the FROM clause of a select.  (INSERT and UPDATE statements are the
+** same as a SELECT with only a single table in the FROM clause.)  For
+** example, if the SQL is this:
+**
+**       SELECT * FROM t1, t2, t3 WHERE ...;
+**
+** Then the code generated is conceptually like the following:
+**
+**      foreach row1 in t1 do       \    Code generated
+**        foreach row2 in t2 do      |-- by sqlite3WhereBegin()
+**          foreach row3 in t3 do   /
+**            ...
+**          end                     \    Code generated
+**        end                        |-- by sqlite3WhereEnd()
+**      end                         /
+**
+** Note that the loops might not be nested in the order in which they
+** appear in the FROM clause if a different order is better able to make
+** use of indices.  Note also that when the IN operator appears in
+** the WHERE clause, it might result in additional nested loops for
+** scanning through all values on the right-hand side of the IN.
+**
+** There are Btree cursors associated with each table.  t1 uses cursor
+** number pTabList->a[0].iCursor.  t2 uses the cursor pTabList->a[1].iCursor.
+** And so forth.  This routine generates code to open those VDBE cursors
+** and sqlite3WhereEnd() generates the code to close them.
+**
+** The code that sqlite3WhereBegin() generates leaves the cursors named
+** in pTabList pointing at their appropriate entries.  The [...] code
+** can use OP_Column and OP_Rowid opcodes on these cursors to extract
+** data from the various tables of the loop.
+**
+** If the WHERE clause is empty, the foreach loops must each scan their
+** entire tables.  Thus a three-way join is an O(N^3) operation.  But if
+** the tables have indices and there are terms in the WHERE clause that
+** refer to those indices, a complete table scan can be avoided and the
+** code will run much faster.  Most of the work of this routine is checking
+** to see if there are indices that can be used to speed up the loop.
+**
+** Terms of the WHERE clause are also used to limit which rows actually
+** make it to the "..." in the middle of the loop.  After each "foreach",
+** terms of the WHERE clause that use only terms in that loop and outer
+** loops are evaluated and if false a jump is made around all subsequent
+** inner loops (or around the "..." if the test occurs within the inner-
+** most loop)
+**
+** OUTER JOINS
+**
+** An outer join of tables t1 and t2 is conceptally coded as follows:
+**
+**    foreach row1 in t1 do
+**      flag = 0
+**      foreach row2 in t2 do
+**        start:
+**          ...
+**          flag = 1
+**      end
+**      if flag==0 then
+**        move the row2 cursor to a null row
+**        goto start
+**      fi
+**    end
+**
+** ORDER BY CLAUSE PROCESSING
+**
+** *ppOrderBy is a pointer to the ORDER BY clause of a SELECT statement,
+** if there is one.  If there is no ORDER BY clause or if this routine
+** is called from an UPDATE or DELETE statement, then ppOrderBy is NULL.
+**
+** If an index can be used so that the natural output order of the table
+** scan is correct for the ORDER BY clause, then that index is used and
+** *ppOrderBy is set to NULL.  This is an optimization that prevents an
+** unnecessary sort of the result set if an index appropriate for the
+** ORDER BY clause already exists.
+**
+** If the where clause loops cannot be arranged to provide the correct
+** output order, then the *ppOrderBy is unchanged.
+*/
+WhereInfo *sqlite3WhereBegin(
+Parse *pParse,        /* The parser context */
+SrcList *pTabList,    /* A list of all tables to be scanned */
+Expr *pWhere,         /* The WHERE clause */
+ExprList **ppOrderBy  /* An ORDER BY clause, or NULL */
+){
+int i;                     /* Loop counter */
+WhereInfo *pWInfo;         /* Will become the return value of this function */
+Vdbe *v = pParse->pVdbe;   /* The virtual database engine */
+int brk, cont = 0;         /* Addresses used during code generation */
+Bitmask notReady;          /* Cursors that are not yet positioned */
+WhereTerm *pTerm;          /* A single term in the WHERE clause */
+ExprMaskSet maskSet;       /* The expression mask set */
+WhereClause wc;            /* The WHERE clause is divided into these terms */
+SrcList::SrcList_item *pTabItem;  /* A single entry from pTabList */
+WhereLevel *pLevel;             /* A single level in the pWInfo list */
+int iFrom;                      /* First unused FROM clause element */
+int andFlags;              /* AND-ed combination of all wc.a[].flags */
+sqlite3 *db;               /* Database connection */
+/* The number of tables in the FROM clause is limited by the number of
+** bits in a Bitmask
+*/
+if( pTabList->nSrc>BMS ){
+sqlite3ErrorMsg(pParse, "at most %d tables in a join", BMS);
+return 0;
+}
+/* Split the WHERE clause into separate subexpressions where each
+** subexpression is separated by an AND operator.
+*/
+initMaskSet(&maskSet);
+whereClauseInit(&wc, pParse, &maskSet);
+whereSplit(&wc, pWhere, TK_AND);
+/* Allocate and initialize the WhereInfo structure that will become the
+** return value.
+*/
+db = pParse->db;
+pWInfo = (WhereInfo*)sqlite3DbMallocZero(db,
+sizeof(WhereInfo) + pTabList->nSrc*sizeof(WhereLevel));
+if( db->mallocFailed ){
+goto whereBeginNoMem;
+}
+pWInfo->nLevel = pTabList->nSrc;
+pWInfo->pParse = pParse;
+pWInfo->pTabList = pTabList;
+pWInfo->iBreak = sqlite3VdbeMakeLabel(v);
+/* Special case: a WHERE clause that is constant.  Evaluate the
+** expression and either jump over all of the code or fall thru.
+*/
+if( pWhere && (pTabList->nSrc==0 || sqlite3ExprIsConstantNotJoin(pWhere)) ){
+sqlite3ExprIfFalse(pParse, pWhere, pWInfo->iBreak, 1);
+pWhere = 0;
+}
+/* Analyze all of the subexpressions.  Note that exprAnalyze() might
+** add new virtual terms onto the end of the WHERE clause.  We do not
+** want to analyze these virtual terms, so start analyzing at the end
+** and work forward so that the added virtual terms are never processed.
+*/
+for(i=0; i<pTabList->nSrc; i++){
+createMask(&maskSet, pTabList->a[i].iCursor);
+}
+exprAnalyzeAll(pTabList, &wc);
+if( db->mallocFailed ){
+goto whereBeginNoMem;
+}
+/* Chose the best index to use for each table in the FROM clause.
+**
+** This loop fills in the following fields:
+**
+**   pWInfo->a[].pIdx      The index to use for this level of the loop.
+**   pWInfo->a[].flags     WHERE_xxx flags associated with pIdx
+**   pWInfo->a[].nEq       The number of == and IN constraints
+**   pWInfo->a[].iFrom     When term of the FROM clause is being coded
+**   pWInfo->a[].iTabCur   The VDBE cursor for the database table
+**   pWInfo->a[].iIdxCur   The VDBE cursor for the index
+**
+** This loop also figures out the nesting order of tables in the FROM
+** clause.
+*/
+notReady = ~(Bitmask)0;
+pTabItem = pTabList->a;
+pLevel = pWInfo->a;
+andFlags = ~0;
+WHERETRACE(("*** Optimizer Start ***\n"));
+for(i=iFrom=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
+Index *pIdx;                /* Index for FROM table at pTabItem */
+int flags;                  /* Flags asssociated with pIdx */
+int nEq;                    /* Number of == or IN constraints */
+double cost;                /* The cost for pIdx */
+int j;                      /* For looping over FROM tables */
+Index *pBest = 0;           /* The best index seen so far */
+int bestFlags = 0;          /* Flags associated with pBest */
+int bestNEq = 0;            /* nEq associated with pBest */
+double lowestCost;          /* Cost of the pBest */
+int bestJ = 0;              /* The value of j */
+Bitmask m;                  /* Bitmask value for j or bestJ */
+int once = 0;               /* True when first table is seen */
+sqlite3_index_info *pIndex; /* Current virtual index */
+lowestCost = SQLITE_BIG_DBL;
+for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
+int doNotReorder;  /* True if this table should not be reordered */
+doNotReorder =  (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;
+if( once && doNotReorder ) break;
+m = getMask(&maskSet, pTabItem->iCursor);
+if( (m & notReady)==0 ){
+if( j==iFrom ) iFrom++;
+continue;
+}
+assert( pTabItem->pTab );
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+if( IsVirtual(pTabItem->pTab) ){
+sqlite3_index_info **ppIdxInfo = &pWInfo->a[j].pIdxInfo;
+cost = bestVirtualIndex(pParse, &wc, pTabItem, notReady,
+ppOrderBy ? *ppOrderBy : 0, i==0,
+ppIdxInfo);
+flags = WHERE_VIRTUALTABLE;
+pIndex = *ppIdxInfo;
+if( pIndex && pIndex->orderByConsumed ){
+flags = WHERE_VIRTUALTABLE | WHERE_ORDERBY;
+}
+pIdx = 0;
+nEq = 0;
+if( (SQLITE_BIG_DBL/2.0)<cost ){
+/* The cost is not allowed to be larger than SQLITE_BIG_DBL (the
+** inital value of lowestCost in this loop. If it is, then
+** the (cost<lowestCost) test below will never be true and
+** pLevel->pBestIdx never set.
+*/
+cost = (SQLITE_BIG_DBL/2.0);
+}
+}else
+#endif
+{
+cost = bestIndex(pParse, &wc, pTabItem, notReady,
+(i==0 && ppOrderBy) ? *ppOrderBy : 0,
+&pIdx, &flags, &nEq);
+pIndex = 0;
+}
+if( cost<lowestCost ){
+once = 1;
+lowestCost = cost;
+pBest = pIdx;
+bestFlags = flags;
+bestNEq = nEq;
+bestJ = j;
+pLevel->pBestIdx = pIndex;
+}
+if( doNotReorder ) break;
+}
+WHERETRACE(("*** Optimizer choose table %d for loop %d\n", bestJ,
+pLevel-pWInfo->a));
+if( (bestFlags & WHERE_ORDERBY)!=0 ){
+*ppOrderBy = 0;
+}
+andFlags &= bestFlags;
+pLevel->flags = bestFlags;
+pLevel->pIdx = pBest;
+pLevel->nEq = bestNEq;
+pLevel->aInLoop = 0;
+pLevel->nIn = 0;
+if( pBest ){
+pLevel->iIdxCur = pParse->nTab++;
+}else{
+pLevel->iIdxCur = -1;
+}
+notReady &= ~getMask(&maskSet, pTabList->a[bestJ].iCursor);
+pLevel->iFrom = bestJ;
+}
+WHERETRACE(("*** Optimizer Finished ***\n"));
+/* If the total query only selects a single row, then the ORDER BY
+** clause is irrelevant.
+*/
+if( (andFlags & WHERE_UNIQUE)!=0 && ppOrderBy ){
+*ppOrderBy = 0;
+}
+/* Open all tables in the pTabList and any indices selected for
+** searching those tables.
+*/
+sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */
+for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
+Table *pTab;     /* Table to open */
+Index *pIx;      /* Index used to access pTab (if any) */
+int iDb;         /* Index of database containing table/index */
+int iIdxCur = pLevel->iIdxCur;
+#ifndef SQLITE_OMIT_EXPLAIN
+if( pParse->explain==2 ){
+char *zMsg;
+	  SrcList::SrcList_item *pItem = &pTabList->a[pLevel->iFrom];
+zMsg = sqlite3MPrintf(db, "TABLE %s", pItem->zName);
+if( pItem->zAlias ){
+zMsg = sqlite3MPrintf(db, "%z AS %s", zMsg, pItem->zAlias);
+}
+if( (pIx = pLevel->pIdx)!=0 ){
+zMsg = sqlite3MPrintf(db, "%z WITH INDEX %s", zMsg, pIx->zName);
+}else if( pLevel->flags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
+zMsg = sqlite3MPrintf(db, "%z USING PRIMARY KEY", zMsg);
+}
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+else if( pLevel->pBestIdx ){
+sqlite3_index_info *pBestIdx = pLevel->pBestIdx;
+zMsg = sqlite3MPrintf(db, "%z VIRTUAL TABLE INDEX %d:%s", zMsg,
+pBestIdx->idxNum, pBestIdx->idxStr);
+}
+#endif
+if( pLevel->flags & WHERE_ORDERBY ){
+zMsg = sqlite3MPrintf(db, "%z ORDER BY", zMsg);
+}
+sqlite3VdbeOp3(v, OP_Explain, i, pLevel->iFrom, zMsg, P3_DYNAMIC);
+}
+#endif /* SQLITE_OMIT_EXPLAIN */
+pTabItem = &pTabList->a[pLevel->iFrom];
+pTab = pTabItem->pTab;
+iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
+if( pTab->isEphem || pTab->pSelect ) continue;
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+if( pLevel->pBestIdx ){
+int iCur = pTabItem->iCursor;
+sqlite3VdbeOp3(v, OP_VOpen, iCur, 0, (const char*)pTab->pVtab, P3_VTAB);
+}else
+#endif
+if( (pLevel->flags & WHERE_IDX_ONLY)==0 ){
+sqlite3OpenTable(pParse, pTabItem->iCursor, iDb, pTab, OP_OpenRead);
+if( pTab->nCol<(sizeof(Bitmask)*8) ){
+Bitmask b = pTabItem->colUsed;
+int n = 0;
+for(; b; b=b>>1, n++){}
+sqlite3VdbeChangeP2(v, sqlite3VdbeCurrentAddr(v)-1, n);
+assert( n<=pTab->nCol );
+}
+}else{
+sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);
+}
+pLevel->iTabCur = pTabItem->iCursor;
+if( (pIx = pLevel->pIdx)!=0 ){
+KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIx);
+assert( pIx->pSchema==pTab->pSchema );
+sqlite3VdbeAddOp(v, OP_Integer, iDb, 0);
+VdbeComment((v, "# %s", pIx->zName));
+sqlite3VdbeOp3(v, OP_OpenRead, iIdxCur, pIx->tnum,
+(char*)pKey, P3_KEYINFO_HANDOFF);
+sqlite3VdbeAddOp(v, OP_SetNumColumns, iIdxCur, pIx->nColumn+1);
+}
+sqlite3CodeVerifySchema(pParse, iDb);
+}
+pWInfo->iTop = sqlite3VdbeCurrentAddr(v);
+/* Generate the code to do the search.  Each iteration of the for
+** loop below generates code for a single nested loop of the VM
+** program.
+*/
+notReady = ~(Bitmask)0;
+for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
+int j;
+int iCur = pTabItem->iCursor;  /* The VDBE cursor for the table */
+Index *pIdx;       /* The index we will be using */
+int nxt;           /* Where to jump to continue with the next IN case */
+int iIdxCur;       /* The VDBE cursor for the index */
+int omitTable;     /* True if we use the index only */
+int bRev;          /* True if we need to scan in reverse order */
+pTabItem = &pTabList->a[pLevel->iFrom];
+iCur = pTabItem->iCursor;
+pIdx = pLevel->pIdx;
+iIdxCur = pLevel->iIdxCur;
+bRev = (pLevel->flags & WHERE_REVERSE)!=0;
+omitTable = (pLevel->flags & WHERE_IDX_ONLY)!=0;
+/* Create labels for the "break" and "continue" instructions
+** for the current loop.  Jump to brk to break out of a loop.
+** Jump to cont to go immediately to the next iteration of the
+** loop.
+**
+** When there is an IN operator, we also have a "nxt" label that
+** means to continue with the next IN value combination.  When
+** there are no IN operators in the constraints, the "nxt" label
+** is the same as "brk".
+*/
+brk = pLevel->brk = pLevel->nxt = sqlite3VdbeMakeLabel(v);
+cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
+/* If this is the right table of a LEFT OUTER JOIN, allocate and
+** initialize a memory cell that records if this table matches any
+** row of the left table of the join.
+*/
+if( pLevel->iFrom>0 && (pTabItem[0].jointype & JT_LEFT)!=0 ){
+if( !pParse->nMem ) pParse->nMem++;
+pLevel->iLeftJoin = pParse->nMem++;
+sqlite3VdbeAddOp(v, OP_MemInt, 0, pLevel->iLeftJoin);
+VdbeComment((v, "# init LEFT JOIN no-match flag"));
+}
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+if( pLevel->pBestIdx ){
+/* Case 0:  The table is a virtual-table.  Use the VFilter and VNext
+**          to access the data.
+*/
+int j;
+sqlite3_index_info *pBestIdx = pLevel->pBestIdx;
+int nConstraint = pBestIdx->nConstraint;
+	  sqlite3_index_info::sqlite3_index_constraint_usage *aUsage =
+pBestIdx->aConstraintUsage;
+	  const sqlite3_index_info::sqlite3_index_constraint *aConstraint =
+pBestIdx->aConstraint;
+for(j=1; j<=nConstraint; j++){
+int k;
+for(k=0; k<nConstraint; k++){
+if( aUsage[k].argvIndex==j ){
+int iTerm = aConstraint[k].iTermOffset;
+sqlite3ExprCode(pParse, wc.a[iTerm].pExpr->pRight);
+break;
+}
+}
+if( k==nConstraint ) break;
+}
+sqlite3VdbeAddOp(v, OP_Integer, j-1, 0);
+sqlite3VdbeAddOp(v, OP_Integer, pBestIdx->idxNum, 0);
+sqlite3VdbeOp3(v, OP_VFilter, iCur, brk, pBestIdx->idxStr,
+pBestIdx->needToFreeIdxStr ? P3_MPRINTF : P3_STATIC);
+pBestIdx->needToFreeIdxStr = 0;
+for(j=0; j<pBestIdx->nConstraint; j++){
+if( aUsage[j].omit ){
+int iTerm = aConstraint[j].iTermOffset;
+disableTerm(pLevel, &wc.a[iTerm]);
+}
+}
+pLevel->op = OP_VNext;
+pLevel->p1 = iCur;
+pLevel->p2 = sqlite3VdbeCurrentAddr(v);
+}else
+#endif /* SQLITE_OMIT_VIRTUALTABLE */
+if( pLevel->flags & WHERE_ROWID_EQ ){
+/* Case 1:  We can directly reference a single row using an
+**          equality comparison against the ROWID field.  Or
+**          we reference multiple rows using a "rowid IN (...)"
+**          construct.
+*/
+pTerm = findTerm(&wc, iCur, -1, notReady, WO_EQ|WO_IN, 0);
+assert( pTerm!=0 );
+assert( pTerm->pExpr!=0 );
+assert( pTerm->leftCursor==iCur );
+assert( omitTable==0 );
+codeEqualityTerm(pParse, pTerm, pLevel);
+nxt = pLevel->nxt;
+sqlite3VdbeAddOp(v, OP_MustBeInt, 1, nxt);
+sqlite3VdbeAddOp(v, OP_NotExists, iCur, nxt);
+VdbeComment((v, "pk"));
+pLevel->op = OP_Noop;
+}else if( pLevel->flags & WHERE_ROWID_RANGE ){
+/* Case 2:  We have an inequality comparison against the ROWID field.
+*/
+int testOp = OP_Noop;
+int start;
+WhereTerm *pStart, *pEnd;
+assert( omitTable==0 );
+pStart = findTerm(&wc, iCur, -1, notReady, WO_GT|WO_GE, 0);
+pEnd = findTerm(&wc, iCur, -1, notReady, WO_LT|WO_LE, 0);
+if( bRev ){
+pTerm = pStart;
+pStart = pEnd;
+pEnd = pTerm;
+}
+if( pStart ){
+Expr *pX;
+pX = pStart->pExpr;
+assert( pX!=0 );
+assert( pStart->leftCursor==iCur );
+sqlite3ExprCode(pParse, pX->pRight);
+sqlite3VdbeAddOp(v, OP_ForceInt, pX->op==TK_LE || pX->op==TK_GT, brk);
+sqlite3VdbeAddOp(v, bRev ? OP_MoveLt : OP_MoveGe, iCur, brk);
+VdbeComment((v, "pk"));
+disableTerm(pLevel, pStart);
+}else{
+sqlite3VdbeAddOp(v, bRev ? OP_Last : OP_Rewind, iCur, brk);
+}
+if( pEnd ){
+Expr *pX;
+pX = pEnd->pExpr;
+assert( pX!=0 );
+assert( pEnd->leftCursor==iCur );
+sqlite3ExprCode(pParse, pX->pRight);
+pLevel->iMem = pParse->nMem++;
+sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
+if( pX->op==TK_LT || pX->op==TK_GT ){
+testOp = bRev ? OP_Le : OP_Ge;
+}else{
+testOp = bRev ? OP_Lt : OP_Gt;
+}
+disableTerm(pLevel, pEnd);
+}
+start = sqlite3VdbeCurrentAddr(v);
+pLevel->op = bRev ? OP_Prev : OP_Next;
+pLevel->p1 = iCur;
+pLevel->p2 = start;
+if( testOp!=OP_Noop ){
+sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);
+sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
+sqlite3VdbeAddOp(v, testOp, SQLITE_AFF_NUMERIC|0x100, brk);
+}
+}else if( pLevel->flags & WHERE_COLUMN_RANGE ){
+/* Case 3: The WHERE clause term that refers to the right-most
+**         column of the index is an inequality.  For example, if
+**         the index is on (x,y,z) and the WHERE clause is of the
+**         form "x=5 AND y<10" then this case is used.  Only the
+**         right-most column can be an inequality - the rest must
+**         use the "==" and "IN" operators.
+**
+**         This case is also used when there are no WHERE clause
+**         constraints but an index is selected anyway, in order
+**         to force the output order to conform to an ORDER BY.
+*/
+int start;
+int nEq = pLevel->nEq;
+int topEq=0;        /* True if top limit uses ==. False is strictly < */
+int btmEq=0;        /* True if btm limit uses ==. False if strictly > */
+int topOp, btmOp;   /* Operators for the top and bottom search bounds */
+int testOp;
+int topLimit = (pLevel->flags & WHERE_TOP_LIMIT)!=0;
+int btmLimit = (pLevel->flags & WHERE_BTM_LIMIT)!=0;
+/* Generate code to evaluate all constraint terms using == or IN
+** and level the values of those terms on the stack.
+*/
+codeAllEqualityTerms(pParse, pLevel, &wc, notReady);
+/* Duplicate the equality term values because they will all be
+** used twice: once to make the termination key and once to make the
+** start key.
+*/
+for(j=0; j<nEq; j++){
+sqlite3VdbeAddOp(v, OP_Dup, nEq-1, 0);
+}
+/* Figure out what comparison operators to use for top and bottom
+** search bounds. For an ascending index, the bottom bound is a > or >=
+** operator and the top bound is a < or <= operator.  For a descending
+** index the operators are reversed.
+*/
+if( pIdx->aSortOrder[nEq]==SQLITE_SO_ASC ){
+topOp = WO_LT|WO_LE;
+btmOp = WO_GT|WO_GE;
+}else{
+topOp = WO_GT|WO_GE;
+btmOp = WO_LT|WO_LE;
+SWAP(int, topLimit, btmLimit);
+}
+/* Generate the termination key.  This is the key value that
+** will end the search.  There is no termination key if there
+** are no equality terms and no "X<..." term.
+**
+** 2002-Dec-04: On a reverse-order scan, the so-called "termination"
+** key computed here really ends up being the start key.
+*/
+nxt = pLevel->nxt;
+if( topLimit ){
+Expr *pX;
+int k = pIdx->aiColumn[j];
+pTerm = findTerm(&wc, iCur, k, notReady, topOp, pIdx);
+assert( pTerm!=0 );
+pX = pTerm->pExpr;
+assert( (pTerm->flags & TERM_CODED)==0 );
+sqlite3ExprCode(pParse, pX->pRight);
+sqlite3VdbeAddOp(v, OP_IsNull, -(nEq*2+1), nxt);
+topEq = pTerm->eOperator & (WO_LE|WO_GE);
+disableTerm(pLevel, pTerm);
+testOp = OP_IdxGE;
+}else{
+testOp = nEq>0 ? OP_IdxGE : OP_Noop;
+topEq = 1;
+}
+if( testOp!=OP_Noop ){
+int nCol = nEq + topLimit;
+pLevel->iMem = pParse->nMem++;
+buildIndexProbe(v, nCol, pIdx);
+if( bRev ){
+int op = topEq ? OP_MoveLe : OP_MoveLt;
+sqlite3VdbeAddOp(v, op, iIdxCur, nxt);
+}else{
+sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
+}
+}else if( bRev ){
+sqlite3VdbeAddOp(v, OP_Last, iIdxCur, brk);
+}
+/* Generate the start key.  This is the key that defines the lower
+** bound on the search.  There is no start key if there are no
+** equality terms and if there is no "X>..." term.  In
+** that case, generate a "Rewind" instruction in place of the
+** start key search.
+**
+** 2002-Dec-04: In the case of a reverse-order search, the so-called
+** "start" key really ends up being used as the termination key.
+*/
+if( btmLimit ){
+Expr *pX;
+int k = pIdx->aiColumn[j];
+pTerm = findTerm(&wc, iCur, k, notReady, btmOp, pIdx);
+assert( pTerm!=0 );
+pX = pTerm->pExpr;
+assert( (pTerm->flags & TERM_CODED)==0 );
+sqlite3ExprCode(pParse, pX->pRight);
+sqlite3VdbeAddOp(v, OP_IsNull, -(nEq+1), nxt);
+btmEq = pTerm->eOperator & (WO_LE|WO_GE);
+disableTerm(pLevel, pTerm);
+}else{
+btmEq = 1;
+}
+if( nEq>0 || btmLimit ){
+int nCol = nEq + btmLimit;
+buildIndexProbe(v, nCol, pIdx);
+if( bRev ){
+pLevel->iMem = pParse->nMem++;
+sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 1);
+testOp = OP_IdxLT;
+}else{
+int op = btmEq ? OP_MoveGe : OP_MoveGt;
+sqlite3VdbeAddOp(v, op, iIdxCur, nxt);
+}
+}else if( bRev ){
+testOp = OP_Noop;
+}else{
+sqlite3VdbeAddOp(v, OP_Rewind, iIdxCur, brk);
+}
+/* Generate the the top of the loop.  If there is a termination
+** key we have to test for that key and abort at the top of the
+** loop.
+*/
+start = sqlite3VdbeCurrentAddr(v);
+if( testOp!=OP_Noop ){
+sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
+sqlite3VdbeAddOp(v, testOp, iIdxCur, nxt);
+if( (topEq && !bRev) || (!btmEq && bRev) ){
+sqlite3VdbeChangeP3(v, -1, "+", P3_STATIC);
+}
+}
+if( topLimit | btmLimit ){
+sqlite3VdbeAddOp(v, OP_Column, iIdxCur, nEq);
+sqlite3VdbeAddOp(v, OP_IsNull, 1, cont);
+}
+if( !omitTable ){
+sqlite3VdbeAddOp(v, OP_IdxRowid, iIdxCur, 0);
+sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);
+}
+/* Record the instruction used to terminate the loop.
+*/
+pLevel->op = bRev ? OP_Prev : OP_Next;
+pLevel->p1 = iIdxCur;
+pLevel->p2 = start;
+}else if( pLevel->flags & WHERE_COLUMN_EQ ){
+/* Case 4:  There is an index and all terms of the WHERE clause that
+**          refer to the index using the "==" or "IN" operators.
+*/
+int start;
+int nEq = pLevel->nEq;
+/* Generate code to evaluate all constraint terms using == or IN
+** and leave the values of those terms on the stack.
+*/
+codeAllEqualityTerms(pParse, pLevel, &wc, notReady);
+nxt = pLevel->nxt;
+/* Generate a single key that will be used to both start and terminate
+** the search
+*/
+buildIndexProbe(v, nEq, pIdx);
+sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 0);
+/* Generate code (1) to move to the first matching element of the table.
+** Then generate code (2) that jumps to "nxt" after the cursor is past
+** the last matching element of the table.  The code (1) is executed
+** once to initialize the search, the code (2) is executed before each
+** iteration of the scan to see if the scan has finished. */
+if( bRev ){
+/* Scan in reverse order */
+sqlite3VdbeAddOp(v, OP_MoveLe, iIdxCur, nxt);
+start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
+sqlite3VdbeAddOp(v, OP_IdxLT, iIdxCur, nxt);
+pLevel->op = OP_Prev;
+}else{
+/* Scan in the forward order */
+sqlite3VdbeAddOp(v, OP_MoveGe, iIdxCur, nxt);
+start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
+sqlite3VdbeOp3(v, OP_IdxGE, iIdxCur, nxt, "+", P3_STATIC);
+pLevel->op = OP_Next;
+}
+if( !omitTable ){
+sqlite3VdbeAddOp(v, OP_IdxRowid, iIdxCur, 0);
+sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);
+}
+pLevel->p1 = iIdxCur;
+pLevel->p2 = start;
+}else{
+/* Case 5:  There is no usable index.  We must do a complete
+**          scan of the entire table.
+*/
+assert( omitTable==0 );
+assert( bRev==0 );
+pLevel->op = OP_Next;
+pLevel->p1 = iCur;
+pLevel->p2 = 1 + sqlite3VdbeAddOp(v, OP_Rewind, iCur, brk);
+}
+notReady &= ~getMask(&maskSet, iCur);
+sqlite3VdbeAddOp(v, OP_StackDepth, -1, 0);
+/* Insert code to test every subexpression that can be completely
+** computed using the current set of tables.
+*/
+for(pTerm=wc.a, j=wc.nTerm; j>0; j--, pTerm++){
+Expr *pE;
+if( pTerm->flags & (TERM_VIRTUAL|TERM_CODED) ) continue;
+if( (pTerm->prereqAll & notReady)!=0 ) continue;
+pE = pTerm->pExpr;
+assert( pE!=0 );
+if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
+continue;
+}
+sqlite3ExprIfFalse(pParse, pE, cont, 1);
+pTerm->flags |= TERM_CODED;
+}
+/* For a LEFT OUTER JOIN, generate code that will record the fact that
+** at least one row of the right table has matched the left table.
+*/
+if( pLevel->iLeftJoin ){
+pLevel->top = sqlite3VdbeCurrentAddr(v);
+sqlite3VdbeAddOp(v, OP_MemInt, 1, pLevel->iLeftJoin);
+VdbeComment((v, "# record LEFT JOIN hit"));
+for(pTerm=wc.a, j=0; j<wc.nTerm; j++, pTerm++){
+if( pTerm->flags & (TERM_VIRTUAL|TERM_CODED) ) continue;
+if( (pTerm->prereqAll & notReady)!=0 ) continue;
+assert( pTerm->pExpr );
+sqlite3ExprIfFalse(pParse, pTerm->pExpr, cont, 1);
+pTerm->flags |= TERM_CODED;
+}
+}
+}
+#ifdef SQLITE_TEST  /* For testing and debugging use only */
+/* Record in the query plan information about the current table
+** and the index used to access it (if any).  If the table itself
+** is not used, its name is just '{}'.  If no index is used
+** the index is listed as "{}".  If the primary key is used the
+** index name is '*'.
+*/
+for(i=0; i<pTabList->nSrc; i++){
+char *z;
+int n;
+pLevel = &pWInfo->a[i];
+pTabItem = &pTabList->a[pLevel->iFrom];
+z = pTabItem->zAlias;
+if( z==0 ) z = pTabItem->pTab->zName;
+n = strlen(z);
+if( n+nQPlan < sizeof(sqlite3_query_plan)-10 ){
+if( pLevel->flags & WHERE_IDX_ONLY ){
+memcpy(&sqlite3_query_plan[nQPlan], "{}", 2);
+nQPlan += 2;
+}else{
+memcpy(&sqlite3_query_plan[nQPlan], z, n);
+nQPlan += n;
+}
+sqlite3_query_plan[nQPlan++] = ' ';
+}
+if( pLevel->flags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
+memcpy(&sqlite3_query_plan[nQPlan], "* ", 2);
+nQPlan += 2;
+}else if( pLevel->pIdx==0 ){
+memcpy(&sqlite3_query_plan[nQPlan], "{} ", 3);
+nQPlan += 3;
+}else{
+n = strlen(pLevel->pIdx->zName);
+if( n+nQPlan < sizeof(sqlite3_query_plan)-2 ){
+memcpy(&sqlite3_query_plan[nQPlan], pLevel->pIdx->zName, n);
+nQPlan += n;
+sqlite3_query_plan[nQPlan++] = ' ';
+}
+}
+}
+while( nQPlan>0 && sqlite3_query_plan[nQPlan-1]==' ' ){
+sqlite3_query_plan[--nQPlan] = 0;
+}
+sqlite3_query_plan[nQPlan] = 0;
+nQPlan = 0;
+#endif /* SQLITE_TEST // Testing and debugging use only */
+/* Record the continuation address in the WhereInfo structure.  Then
+** clean up and return.
+*/
+pWInfo->iContinue = cont;
+whereClauseClear(&wc);
+return pWInfo;
+/* Jump here if malloc fails */
+whereBeginNoMem:
+whereClauseClear(&wc);
+whereInfoFree(pWInfo);
+return 0;
+}
+/*
+** Generate the end of the WHERE loop.  See comments on
+** sqlite3WhereBegin() for additional information.
+*/
+void sqlite3WhereEnd(WhereInfo *pWInfo){
+Vdbe *v = pWInfo->pParse->pVdbe;
+int i;
+WhereLevel *pLevel;
+SrcList *pTabList = pWInfo->pTabList;
+/* Generate loop termination code.
+*/
+for(i=pTabList->nSrc-1; i>=0; i--){
+pLevel = &pWInfo->a[i];
+sqlite3VdbeResolveLabel(v, pLevel->cont);
+if( pLevel->op!=OP_Noop ){
+sqlite3VdbeAddOp(v, pLevel->op, pLevel->p1, pLevel->p2);
+}
+if( pLevel->nIn ){
+		WhereLevel::InLoop *pIn;
+int j;
+sqlite3VdbeResolveLabel(v, pLevel->nxt);
+for(j=pLevel->nIn, pIn=&pLevel->aInLoop[j-1]; j>0; j--, pIn--){
+sqlite3VdbeJumpHere(v, pIn->topAddr+1);
+sqlite3VdbeAddOp(v, OP_Next, pIn->iCur, pIn->topAddr);
+sqlite3VdbeJumpHere(v, pIn->topAddr-1);
+}
+sqlite3_free(pLevel->aInLoop);
+}
+sqlite3VdbeResolveLabel(v, pLevel->brk);
+if( pLevel->iLeftJoin ){
+int addr;
+addr = sqlite3VdbeAddOp(v, OP_IfMemPos, pLevel->iLeftJoin, 0);
+sqlite3VdbeAddOp(v, OP_NullRow, pTabList->a[i].iCursor, 0);
+if( pLevel->iIdxCur>=0 ){
+sqlite3VdbeAddOp(v, OP_NullRow, pLevel->iIdxCur, 0);
+}
+sqlite3VdbeAddOp(v, OP_Goto, 0, pLevel->top);
+sqlite3VdbeJumpHere(v, addr);
+}
+}
+/* The "break" point is here, just past the end of the outer loop.
+** Set it.
+*/
+sqlite3VdbeResolveLabel(v, pWInfo->iBreak);
+/* Close all of the cursors that were opened by sqlite3WhereBegin.
+*/
+for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
+	  SrcList::SrcList_item *pTabItem = &pTabList->a[pLevel->iFrom];
+Table *pTab = pTabItem->pTab;
+assert( pTab!=0 );
+if( pTab->isEphem || pTab->pSelect ) continue;
+if( (pLevel->flags & WHERE_IDX_ONLY)==0 ){
+sqlite3VdbeAddOp(v, OP_Close, pTabItem->iCursor, 0);
+}
+if( pLevel->pIdx!=0 ){
+sqlite3VdbeAddOp(v, OP_Close, pLevel->iIdxCur, 0);
+}
+/* If this scan uses an index, make code substitutions to read data
+** from the index in preference to the table. Sometimes, this means
+** the table need never be read from. This is a performance boost,
+** as the vdbe level waits until the table is read before actually
+** seeking the table cursor to the record corresponding to the current
+** position in the index.
+**
+** Calls to the code generator in between sqlite3WhereBegin and
+** sqlite3WhereEnd will have created code that references the table
+** directly.  This loop scans all that code looking for opcodes
+** that reference the table and converts them into opcodes that
+** reference the index.
+*/
+if( pLevel->pIdx ){
+int k, j, last;
+VdbeOp *pOp;
+Index *pIdx = pLevel->pIdx;
+int useIndexOnly = pLevel->flags & WHERE_IDX_ONLY;
+assert( pIdx!=0 );
+pOp = sqlite3VdbeGetOp(v, pWInfo->iTop);
+last = sqlite3VdbeCurrentAddr(v);
+for(k=pWInfo->iTop; k<last; k++, pOp++){
+if( pOp->p1!=pLevel->iTabCur ) continue;
+if( pOp->opcode==OP_Column ){
+for(j=0; j<pIdx->nColumn; j++){
+if( pOp->p2==pIdx->aiColumn[j] ){
+pOp->p2 = j;
+pOp->p1 = pLevel->iIdxCur;
+break;
+}
+}
+assert(!useIndexOnly || j<pIdx->nColumn);
+}else if( pOp->opcode==OP_Rowid ){
+pOp->p1 = pLevel->iIdxCur;
+pOp->opcode = OP_IdxRowid;
+}else if( pOp->opcode==OP_NullRow && useIndexOnly ){
+pOp->opcode = OP_Noop;
+}
+}
+}
+}
+/* Final cleanup
+*/
+whereInfoFree(pWInfo);
+return;
+}