diff -r 000000000000 -r dd21522fd290 webengine/webkitutils/SqliteSymbian/where.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/webengine/webkitutils/SqliteSymbian/where.c	Mon Mar 30 12:54:55 2009 +0300
@@ -0,0 +1,2543 @@
+/*
+** 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.c,v 1.228 2006/06/27 13:20:22 drh Exp $
+*/
+#include "sqliteInt.h"
+
+/*
+** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
+*/
+#define BMS  (sizeof(Bitmask)*8)
+
+/*
+** Determine the number of elements in an array.
+*/
+#define ARRAYSIZE(X)  (sizeof(X)/sizeof(X[0]))
+
+/*
+** Trace output macros
+*/
+#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
+int sqlite3_where_trace = 0;
+# define TRACE(X)  if(sqlite3_where_trace) sqlite3DebugPrintf X
+#else
+# define TRACE(X)
+#endif
+
+/* Forward reference
+*/
+typedef struct WhereClause WhereClause;
+
+/*
+** 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 */
+  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.
+*/
+typedef struct ExprMaskSet ExprMaskSet;
+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
+
+/*
+** Value for flags returned by bestIndex()
+*/
+#define WHERE_ROWID_EQ       0x0001   /* rowid=EXPR or rowid IN (...) */
+#define WHERE_ROWID_RANGE    0x0002   /* rowid<EXPR and/or rowid>EXPR */
+#define WHERE_COLUMN_EQ      0x0010   /* x=EXPR or x IN (...) */
+#define WHERE_COLUMN_RANGE   0x0020   /* x<EXPR and/or x>EXPR */
+#define WHERE_COLUMN_IN      0x0040   /* x IN (...) */
+#define WHERE_TOP_LIMIT      0x0100   /* x<EXPR or x<=EXPR constraint */
+#define WHERE_BTM_LIMIT      0x0200   /* x>EXPR or x>=EXPR constraint */
+#define WHERE_IDX_ONLY       0x0800   /* Use index only - omit table */
+#define WHERE_ORDERBY        0x1000   /* Output will appear in correct order */
+#define WHERE_REVERSE        0x2000   /* Scan in reverse order */
+#define WHERE_UNIQUE         0x4000   /* Selects no more than one row */
+#define WHERE_VIRTUALTABLE   0x8000   /* Use virtual-table processing */
+
+/*
+** Initialize a preallocated WhereClause structure.
+*/
+static void whereClauseInit(WhereClause *pWC, Parse *pParse){
+  pWC->pParse = pParse;
+  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 ){
+    sqliteFree(pWC->a);
+  }
+}
+
+/*
+** Add a new entries to the WhereClause structure.  Increase the allocated
+** space as necessary.
+**
+** 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 = sqliteMalloc( sizeof(pWC->a[0])*pWC->nSlot*2 );
+    if( pWC->a==0 ) return 0;
+    memcpy(pWC->a, pOld, sizeof(pWC->a[0])*pWC->nTerm);
+    if( pOld!=pWC->aStatic ){
+      sqliteFree(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;
+  if( pS==0 ){
+    mask = 0;
+  }else{
+    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);
+  }
+  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);
+}
+
+/*
+** 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".
+*/
+static void exprCommute(Expr *pExpr){
+  assert( allowedOp(pExpr->op) && pExpr->op!=TK_IN );
+  SWAP(CollSeq*,pExpr->pRight->pColl,pExpr->pLeft->pColl);
+  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{
+    c = WO_EQ<<(op-TK_EQ);
+  }
+  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 ){
+        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;
+        pColl = sqlite3ExprCollSeq(pParse, pX->pLeft);
+        if( !pColl ){
+          if( pX->pRight ){
+            pColl = sqlite3ExprCollSeq(pParse, 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*, ExprMaskSet*, WhereClause*, int);
+
+/*
+** Call exprAnalyze on all terms in a WHERE clause.  
+**
+**
+*/
+static void exprAnalyzeAll(
+  SrcList *pTabList,       /* the FROM clause */
+  ExprMaskSet *pMaskSet,   /* table masks */
+  WhereClause *pWC         /* the WHERE clause to be analyzed */
+){
+  int i;
+  for(i=pWC->nTerm-1; i>=0; i--){
+    exprAnalyze(pTabList, pMaskSet, 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 ){
+    pColl = db->pDfltColl;
+  }
+  if( (pColl->type!=SQLITE_COLL_BINARY || noCase) &&
+      (pColl->type!=SQLITE_COLL_NOCASE || !noCase) ){
+    return 0;
+  }
+  sqlite3DequoteExpr(pRight);
+  z = (char *)pRight->token.z;
+  for(cnt=0; (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;
+}
+
+
+/*
+** 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 */
+  ExprMaskSet *pMaskSet,    /* table masks */
+  WhereClause *pWC,         /* the WHERE clause */
+  int idxTerm               /* Index of the term to be analyzed */
+){
+  WhereTerm *pTerm = &pWC->a[idxTerm];
+  Expr *pExpr = pTerm->pExpr;
+  Bitmask prereqLeft;
+  Bitmask prereqAll;
+  int nPattern;
+  int isComplete;
+
+  if( sqlite3MallocFailed() ) return;
+  prereqLeft = exprTableUsage(pMaskSet, pExpr->pLeft);
+  if( pExpr->op==TK_IN ){
+    assert( pExpr->pRight==0 );
+    pTerm->prereqRight = exprListTableUsage(pMaskSet, pExpr->pList)
+                          | exprSelectTableUsage(pMaskSet, pExpr->pSelect);
+  }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(pExpr->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(pExpr->op);
+    }
+    if( pRight && pRight->op==TK_COLUMN ){
+      WhereTerm *pNew;
+      Expr *pDup;
+      if( pTerm->leftCursor>=0 ){
+        int idxNew;
+        pDup = sqlite3ExprDup(pExpr);
+        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(ops[i], sqlite3ExprDup(pExpr->pLeft),
+                             sqlite3ExprDup(pList->a[i].pExpr), 0);
+      idxNew = whereClauseInsert(pWC, pNewExpr, TERM_VIRTUAL|TERM_DYNAMIC);
+      exprAnalyze(pSrc, pMaskSet, 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);
+    whereSplit(&sOr, pExpr, TK_OR);
+    exprAnalyzeAll(pSrc, pMaskSet, &sOr);
+    assert( sOr.nTerm>0 );
+    j = 0;
+    do{
+      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( pOrTerm->leftCursor==iCursor && pOrTerm->leftColumn==iColumn ){
+          pOrTerm->flags |= TERM_OR_OK;
+        }else if( (pOrTerm->flags & TERM_COPIED)!=0 ||
+                    ((pOrTerm->flags & TERM_VIRTUAL)!=0 &&
+                     (sOr.a[pOrTerm->iParent].flags & TERM_OR_OK)!=0) ){
+          pOrTerm->flags &= ~TERM_OR_OK;
+        }else{
+          ok = 0;
+        }
+      }
+    }while( !ok && (sOr.a[j++].flags & TERM_COPIED)!=0 && j<sOr.nTerm );
+    if( ok ){
+      ExprList *pList = 0;
+      Expr *pNew, *pDup;
+      for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0 && ok; i--, pOrTerm++){
+        if( (pOrTerm->flags & TERM_OR_OK)==0 ) continue;
+        pDup = sqlite3ExprDup(pOrTerm->pExpr->pRight);
+        pList = sqlite3ExprListAppend(pList, pDup, 0);
+      }
+      pDup = sqlite3Expr(TK_COLUMN, 0, 0, 0);
+      if( pDup ){
+        pDup->iTable = iCursor;
+        pDup->iColumn = iColumn;
+      }
+      pNew = sqlite3Expr(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, pMaskSet, 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(pWC->pParse->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 = sqlite3Expr(TK_STRING, 0, 0, 0);
+    if( pStr1 ){
+      sqlite3TokenCopy(&pStr1->token, &pRight->token);
+      pStr1->token.n = nPattern;
+    }
+    pStr2 = sqlite3ExprDup(pStr1);
+    if( pStr2 ){
+      assert( pStr2->token.dyn );
+      ++*(u8*)&pStr2->token.z[nPattern-1];
+    }
+    pNewExpr1 = sqlite3Expr(TK_GE, sqlite3ExprDup(pLeft), pStr1, 0);
+    idxNew1 = whereClauseInsert(pWC, pNewExpr1, TERM_VIRTUAL|TERM_DYNAMIC);
+    exprAnalyze(pSrc, pMaskSet, pWC, idxNew1);
+    pNewExpr2 = sqlite3Expr(TK_LT, sqlite3ExprDup(pLeft), pStr2, 0);
+    idxNew2 = whereClauseInsert(pWC, pNewExpr2, TERM_VIRTUAL|TERM_DYNAMIC);
+    exprAnalyze(pSrc, pMaskSet, 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(TK_MATCH, 0, sqlite3ExprDup(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 */
+}
+
+
+/*
+** 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 */
+  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 */
+  struct 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.
+  */
+  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 */
+
+    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 */
+      return 0;
+    }
+    pColl = sqlite3ExprCollSeq(pParse, pExpr);
+    if( !pColl ) pColl = db->pDfltColl;
+    if( pExpr->iColumn!=pIdx->aiColumn[i] || 
+        sqlite3StrICmp(pColl->zName, pIdx->azColl[i]) ){
+      /* 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( pIdx->aSortOrder[i]==0 || pIdx->aSortOrder[i]==1 );
+    termSortOrder = pIdx->aSortOrder[i] ^ 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++;
+  }
+
+  /* The index can be used for sorting if all terms of the ORDER BY clause
+  ** are covered.
+  */
+  if( j>=nTerm ){
+    *pbRev = sortOrder!=0;
+    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 */
+  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( pOrderBy->nExpr==1 && p->op==TK_COLUMN && p->iTable==base
+          && p->iColumn==-1 ){
+    *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_TEST) || 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 */
+  struct 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;
+  struct sqlite3_index_constraint *pIdxCons;
+  struct sqlite3_index_orderby *pIdxOrderBy;
+  struct 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;
+    TRACE(("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;
+      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 = sqliteMalloc( 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 = (struct sqlite3_index_constraint*)&pIdxInfo[1];
+    pIdxOrderBy = (struct sqlite3_index_orderby*)&pIdxCons[nTerm];
+    pUsage = (struct sqlite3_index_constraint_usage*)&pIdxOrderBy[nOrderBy];
+    *(int*)&pIdxInfo->nConstraint = nTerm;
+    *(int*)&pIdxInfo->nOrderBy = nOrderBy;
+    *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint = pIdxCons;
+    *(struct sqlite3_index_orderby**)&pIdxInfo->aOrderBy = pIdxOrderBy;
+    *(struct 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;
+      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 */
+  assert( pTab->azModuleArg && pTab->azModuleArg[0] );
+  if( pTab->pVtab==0 ){
+    sqlite3ErrorMsg(pParse, "undefined module %s for table %s",
+        pTab->azModuleArg[0], pTab->zName);
+    return 0.0;
+  }
+
+  /* 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 = *(struct 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);
+  TRACE(("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 ){
+      sqlite3FailedMalloc();
+    }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 */
+  struct 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 */
+  double cost;                /* Cost of using pProbe */
+
+  TRACE(("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, &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;
+      TRACE(("... 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;
+    }
+    TRACE(("... 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;
+  TRACE(("... 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 */
+    }
+    TRACE(("... 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, &rev) ){
+      flags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;
+      if( rev ){
+        flags |= WHERE_REVERSE;
+      }
+    }else{
+      cost += cost*estLog(cost);
+      TRACE(("... sorting increases cost to %.9g\n", cost));
+    }
+  }
+  if( cost<lowestCost ){
+    lowestCost = cost;
+    bestFlags = flags;
+  }
+
+  /* Look at each index.
+  */
+  for(; pProbe; pProbe=pProbe->pNext){
+    int i;                       /* Loop counter */
+    double inMultiplier = 1;
+
+    TRACE(("... 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, WO_EQ|WO_IN, 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;
+    }
+    TRACE(("...... 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;
+        }
+        TRACE(("...... 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,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);
+        TRACE(("...... 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;
+        TRACE(("...... idx-only reduces cost to %.9g\n", cost));
+      }
+    }
+
+    /* If this index has achieved the lowest cost so far, then use it.
+    */
+    if( cost < lowestCost ){
+      bestIdx = pProbe;
+      lowestCost = cost;
+      assert( flags!=0 );
+      bestFlags = flags;
+      bestNEq = nEq;
+    }
+  }
+
+  /* Report the best result
+  */
+  *ppIndex = bestIdx;
+  TRACE(("best index is %s, cost=%.9g, flags=%x, nEq=%d\n",
+        bestIdx ? bestIdx->zName : "(none)", lowestCost, bestFlags, bestNEq));
+  *pFlags = bestFlags;
+  *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.  Details:
+**
+**    *  Check the top nColumn entries on the stack.  If any
+**       of those entries are NULL, jump immediately to brk,
+**       which is the loop exit, since no index entry will match
+**       if any part of the key is NULL. Pop (nColumn+nExtra) 
+**       elements from the stack.
+**
+**    *  Construct a probe entry from the top nColumn entries in
+**       the stack with affinities appropriate for index pIdx. 
+**       Only nColumn elements are popped from the stack in this case
+**       (by OP_MakeRecord).
+**
+*/
+static void buildIndexProbe(
+  Vdbe *v, 
+  int nColumn, 
+  int nExtra, 
+  int brk, 
+  Index *pIdx
+){
+  sqlite3VdbeAddOp(v, OP_NotNull, -nColumn, sqlite3VdbeCurrentAddr(v)+3);
+  sqlite3VdbeAddOp(v, OP_Pop, nColumn+nExtra, 0);
+  sqlite3VdbeAddOp(v, OP_Goto, 0, brk);
+  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 */
+  int brk,            /* Jump here to abandon the loop */
+  WhereLevel *pLevel  /* When level of the FROM clause we are working on */
+){
+  Expr *pX = pTerm->pExpr;
+  if( pX->op!=TK_IN ){
+    assert( pX->op==TK_EQ );
+    sqlite3ExprCode(pParse, pX->pRight);
+#ifndef SQLITE_OMIT_SUBQUERY
+  }else{
+    int iTab;
+    int *aIn;
+    Vdbe *v = pParse->pVdbe;
+
+    sqlite3CodeSubselect(pParse, pX);
+    iTab = pX->iTable;
+    sqlite3VdbeAddOp(v, OP_Rewind, iTab, 0);
+    VdbeComment((v, "# %.*s", pX->span.n, pX->span.z));
+    pLevel->nIn++;
+    sqliteReallocOrFree((void**)&pLevel->aInLoop,
+                                 sizeof(pLevel->aInLoop[0])*2*pLevel->nIn);
+    aIn = pLevel->aInLoop;
+    if( aIn ){
+      aIn += pLevel->nIn*2 - 2;
+      aIn[0] = iTab;
+      aIn[1] = sqlite3VdbeAddOp(v, OP_Column, iTab, 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 brk               /* Jump here to end the loop */
+){
+  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
+  */
+  for(j=0; j<pIdx->nColumn; j++){
+    int k = pIdx->aiColumn[j];
+    pTerm = findTerm(pWC, iCur, k, notReady, WO_EQ|WO_IN, pIdx);
+    if( pTerm==0 ) break;
+    assert( (pTerm->flags & TERM_CODED)==0 );
+    codeEqualityTerm(pParse, pTerm, brk, pLevel);
+    if( termsInMem ){
+      sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem+j+1, 1);
+    }
+  }
+  assert( j==nEq );
+
+  /* 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 ){
+          sqlite3_free(pInfo->idxStr);
+        }
+        sqliteFree(pInfo);
+      }
+    }
+    sqliteFree(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 */
+  struct 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 */
+
+  /* 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);
+  whereSplit(&wc, pWhere, TK_AND);
+    
+  /* Allocate and initialize the WhereInfo structure that will become the
+  ** return value.
+  */
+  pWInfo = sqliteMalloc( sizeof(WhereInfo) + pTabList->nSrc*sizeof(WhereLevel));
+  if( sqlite3MallocFailed() ){
+    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 || sqlite3ExprIsConstant(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, &maskSet, &wc);
+  if( sqlite3MallocFailed() ){
+    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;
+  TRACE(("*** 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
+                   || (j>0 && (pTabItem[-1].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;
+      }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;
+    }
+    TRACE(("*** 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;
+  }
+  TRACE(("*** 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;
+      struct SrcList_item *pItem = &pTabList->a[pLevel->iFrom];
+      zMsg = sqlite3MPrintf("TABLE %s", pItem->zName);
+      if( pItem->zAlias ){
+        zMsg = sqlite3MPrintf("%z AS %s", zMsg, pItem->zAlias);
+      }
+      if( (pIx = pLevel->pIdx)!=0 ){
+        zMsg = sqlite3MPrintf("%z WITH INDEX %s", zMsg, pIx->zName);
+      }else if( pLevel->flags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
+        zMsg = sqlite3MPrintf("%z USING PRIMARY KEY", zMsg);
+      }
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+      else if( pLevel->pBestIdx ){
+        sqlite3_index_info *pBestIdx = pLevel->pBestIdx;
+        zMsg = sqlite3MPrintf("%z VIRTUAL TABLE INDEX %d:%s", zMsg,
+                    pBestIdx->idxNum, pBestIdx->idxStr);
+      }
+#endif
+      if( pLevel->flags & WHERE_ORDERBY ){
+        zMsg = sqlite3MPrintf("%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);
+    }
+    if( (pLevel->flags & WHERE_IDX_ONLY)!=0 ){
+      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 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.
+    */
+    brk = pLevel->brk = 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[-1].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;
+      struct sqlite3_index_constraint_usage *aUsage =
+                                                  pBestIdx->aConstraintUsage;
+      const struct 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, brk, pLevel);
+      sqlite3VdbeAddOp(v, OP_MustBeInt, 1, brk);
+      sqlite3VdbeAddOp(v, OP_NotExists, iCur, brk);
+      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, 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 nNotNull;       /* Number of rows of index that must be non-NULL */
+      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, brk);
+
+      /* 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.
+      */
+      nNotNull = nEq + topLimit;
+      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.
+      */
+      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);
+        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, nEq, brk, pIdx);
+        if( bRev ){
+          int op = topEq ? OP_MoveLe : OP_MoveLt;
+          sqlite3VdbeAddOp(v, op, iIdxCur, brk);
+        }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);
+        btmEq = pTerm->eOperator & (WO_LE|WO_GE);
+        disableTerm(pLevel, pTerm);
+      }else{
+        btmEq = 1;
+      }
+      if( nEq>0 || btmLimit ){
+        int nCol = nEq + btmLimit;
+        buildIndexProbe(v, nCol, 0, brk, 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, brk);
+        }
+      }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, brk);
+        if( (topEq && !bRev) || (!btmEq && bRev) ){
+          sqlite3VdbeChangeP3(v, -1, "+", P3_STATIC);
+        }
+      }
+      sqlite3VdbeAddOp(v, OP_RowKey, iIdxCur, 0);
+      sqlite3VdbeAddOp(v, OP_IdxIsNull, nNotNull, 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, brk);
+
+      /* Generate a single key that will be used to both start and terminate
+      ** the search
+      */
+      buildIndexProbe(v, nEq, 0, brk, 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 "brk" 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, brk);
+        start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
+        sqlite3VdbeAddOp(v, OP_IdxLT, iIdxCur, brk);
+        pLevel->op = OP_Prev;
+      }else{
+        /* Scan in the forward order */
+        sqlite3VdbeAddOp(v, OP_MoveGe, iIdxCur, brk);
+        start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
+        sqlite3VdbeOp3(v, OP_IdxGE, iIdxCur, brk, "+", P3_STATIC);
+        pLevel->op = OP_Next;
+      }
+      sqlite3VdbeAddOp(v, OP_RowKey, iIdxCur, 0);
+      sqlite3VdbeAddOp(v, OP_IdxIsNull, nEq, cont);
+      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);
+
+    /* 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 ){
+        strcpy(&sqlite3_query_plan[nQPlan], "{}");
+        nQPlan += 2;
+      }else{
+        strcpy(&sqlite3_query_plan[nQPlan], z);
+        nQPlan += n;
+      }
+      sqlite3_query_plan[nQPlan++] = ' ';
+    }
+    if( pLevel->flags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
+      strcpy(&sqlite3_query_plan[nQPlan], "* ");
+      nQPlan += 2;
+    }else if( pLevel->pIdx==0 ){
+      strcpy(&sqlite3_query_plan[nQPlan], "{} ");
+      nQPlan += 3;
+    }else{
+      n = strlen(pLevel->pIdx->zName);
+      if( n+nQPlan < sizeof(sqlite3_query_plan)-2 ){
+        strcpy(&sqlite3_query_plan[nQPlan], pLevel->pIdx->zName);
+        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);
+    }
+    sqlite3VdbeResolveLabel(v, pLevel->brk);
+    if( pLevel->nIn ){
+      int *a;
+      int j;
+      for(j=pLevel->nIn, a=&pLevel->aInLoop[j*2-2]; j>0; j--, a-=2){
+        sqlite3VdbeAddOp(v, OP_Next, a[0], a[1]);
+        sqlite3VdbeJumpHere(v, a[1]-1);
+      }
+      sqliteFree(pLevel->aInLoop);
+    }
+    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++){
+    struct 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);
+    }
+
+    /* Make cursor substitutions for cases where we want to use
+    ** just the index and never reference the table.
+    ** 
+    ** 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->flags & WHERE_IDX_ONLY ){
+      int k, j, last;
+      VdbeOp *pOp;
+      Index *pIdx = pLevel->pIdx;
+
+      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 ){
+          pOp->p1 = pLevel->iIdxCur;
+          for(j=0; j<pIdx->nColumn; j++){
+            if( pOp->p2==pIdx->aiColumn[j] ){
+              pOp->p2 = j;
+              break;
+            }
+          }
+        }else if( pOp->opcode==OP_Rowid ){
+          pOp->p1 = pLevel->iIdxCur;
+          pOp->opcode = OP_IdxRowid;
+        }else if( pOp->opcode==OP_NullRow ){
+          pOp->opcode = OP_Noop;
+        }
+      }
+    }
+  }
+
+  /* Final cleanup
+  */
+  whereInfoFree(pWInfo);
+  return;
+}