/*

** 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 file contains C code routines that are called by the parser

** in order to generate code for DELETE FROM statements.

**

** $Id: delete.c,v 1.127 2006/06/19 03:05:10 danielk1977 Exp $

*/

#include "sqliteInt.h"

/*

** Look up every table that is named in pSrc.  If any table is not found,

** add an error message to pParse->zErrMsg and return NULL.  If all tables

** are found, return a pointer to the last table.

*/

Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){

  Table *pTab = 0;

  int i;

  struct SrcList_item *pItem;

  for(i=0, pItem=pSrc->a; i<pSrc->nSrc; i++, pItem++){

    pTab = sqlite3LocateTable(pParse, pItem->zName, pItem->zDatabase);

    sqlite3DeleteTable(pParse->db, pItem->pTab);

    pItem->pTab = pTab;

    if( pTab ){

      pTab->nRef++;

    }

  }

  return pTab;

}

/*

** Check to make sure the given table is writable.  If it is not

** writable, generate an error message and return 1.  If it is

** writable return 0;

*/

int sqlite3IsReadOnly(Parse *pParse, Table *pTab, int viewOk){

  if( (pTab->readOnly && (pParse->db->flags & SQLITE_WriteSchema)==0

        && pParse->nested==0) 

#ifndef SQLITE_OMIT_VIRTUALTABLE

      || (pTab->pMod && pTab->pMod->pModule->xUpdate==0)

#endif

  ){

    sqlite3ErrorMsg(pParse, "table %s may not be modified", pTab->zName);

    return 1;

  }

#ifndef SQLITE_OMIT_VIEW

  if( !viewOk && pTab->pSelect ){

    sqlite3ErrorMsg(pParse,"cannot modify %s because it is a view",pTab->zName);

    return 1;

  }

#endif

  return 0;

}

/*

** Generate code that will open a table for reading.

*/

void sqlite3OpenTable(

  Parse *p,       /* Generate code into this VDBE */

  int iCur,       /* The cursor number of the table */

  int iDb,        /* The database index in sqlite3.aDb[] */

  Table *pTab,    /* The table to be opened */

  int opcode      /* OP_OpenRead or OP_OpenWrite */

){

  Vdbe *v;

  if( IsVirtual(pTab) ) return;

  v = sqlite3GetVdbe(p);

  assert( opcode==OP_OpenWrite || opcode==OP_OpenRead );

  sqlite3TableLock(p, iDb, pTab->tnum, (opcode==OP_OpenWrite), pTab->zName);

  sqlite3VdbeAddOp(v, OP_Integer, iDb, 0);

  VdbeComment((v, "# %s", pTab->zName));

  sqlite3VdbeAddOp(v, opcode, iCur, pTab->tnum);

  sqlite3VdbeAddOp(v, OP_SetNumColumns, iCur, pTab->nCol);

}

/*

** Generate code for a DELETE FROM statement.

**

**     DELETE FROM table_wxyz WHERE a<5 AND b NOT NULL;

**                 \________/       \________________/

**                  pTabList              pWhere

*/

void sqlite3DeleteFrom(

  Parse *pParse,         /* The parser context */

  SrcList *pTabList,     /* The table from which we should delete things */

  Expr *pWhere           /* The WHERE clause.  May be null */

){

  Vdbe *v;               /* The virtual database engine */

  Table *pTab;           /* The table from which records will be deleted */

  const char *zDb;       /* Name of database holding pTab */

  int end, addr = 0;     /* A couple addresses of generated code */

  int i;                 /* Loop counter */

  WhereInfo *pWInfo;     /* Information about the WHERE clause */

  Index *pIdx;           /* For looping over indices of the table */

  int iCur;              /* VDBE Cursor number for pTab */

  sqlite3 *db;           /* Main database structure */

  AuthContext sContext;  /* Authorization context */

  int oldIdx = -1;       /* Cursor for the OLD table of AFTER triggers */

  NameContext sNC;       /* Name context to resolve expressions in */

  int iDb;

#ifndef SQLITE_OMIT_TRIGGER

  int isView;                  /* True if attempting to delete from a view */

  int triggers_exist = 0;      /* True if any triggers exist */

#endif

  sContext.pParse = 0;

  if( pParse->nErr || sqlite3MallocFailed() ){

    goto delete_from_cleanup;

  }

  db = pParse->db;

  assert( pTabList->nSrc==1 );

  /* Locate the table which we want to delete.  This table has to be

  ** put in an SrcList structure because some of the subroutines we

  ** will be calling are designed to work with multiple tables and expect

  ** an SrcList* parameter instead of just a Table* parameter.

  */

  pTab = sqlite3SrcListLookup(pParse, pTabList);

  if( pTab==0 )  goto delete_from_cleanup;

  /* Figure out if we have any triggers and if the table being

  ** deleted from is a view

  */

#ifndef SQLITE_OMIT_TRIGGER

  triggers_exist = sqlite3TriggersExist(pParse, pTab, TK_DELETE, 0);

  isView = pTab->pSelect!=0;

#else

# define triggers_exist 0

# define isView 0

#endif

#ifdef SQLITE_OMIT_VIEW

# undef isView

# define isView 0

#endif

  if( sqlite3IsReadOnly(pParse, pTab, triggers_exist) ){

    goto delete_from_cleanup;

  }

  iDb = sqlite3SchemaToIndex(db, pTab->pSchema);

  assert( iDb<db->nDb );

  zDb = db->aDb[iDb].zName;

  if( sqlite3AuthCheck(pParse, SQLITE_DELETE, pTab->zName, 0, zDb) ){

    goto delete_from_cleanup;

  }

  /* If pTab is really a view, make sure it has been initialized.

  */

  if( sqlite3ViewGetColumnNames(pParse, pTab) ){

    goto delete_from_cleanup;

  }

  /* Allocate a cursor used to store the old.* data for a trigger.

  */

  if( triggers_exist ){ 

    oldIdx = pParse->nTab++;

  }

  /* Resolve the column names in the WHERE clause.

  */

  assert( pTabList->nSrc==1 );

  iCur = pTabList->a[0].iCursor = pParse->nTab++;

  memset(&sNC, 0, sizeof(sNC));

  sNC.pParse = pParse;

  sNC.pSrcList = pTabList;

  if( sqlite3ExprResolveNames(&sNC, pWhere) ){

    goto delete_from_cleanup;

  }

  /* Start the view context

  */

  if( isView ){

    sqlite3AuthContextPush(pParse, &sContext, pTab->zName);

  }

  /* Begin generating code.

  */

  v = sqlite3GetVdbe(pParse);

  if( v==0 ){

    goto delete_from_cleanup;

  }

  if( pParse->nested==0 ) sqlite3VdbeCountChanges(v);

  sqlite3BeginWriteOperation(pParse, triggers_exist, iDb);

  /* If we are trying to delete from a view, realize that view into

  ** a ephemeral table.

  */

  if( isView ){

    Select *pView = sqlite3SelectDup(pTab->pSelect);

    sqlite3Select(pParse, pView, SRT_EphemTab, iCur, 0, 0, 0, 0);

    sqlite3SelectDelete(pView);

  }

  /* Initialize the counter of the number of rows deleted, if

  ** we are counting rows.

  */

  if( db->flags & SQLITE_CountRows ){

    sqlite3VdbeAddOp(v, OP_Integer, 0, 0);

  }

  /* Special case: A DELETE without a WHERE clause deletes everything.

  ** It is easier just to erase the whole table.  Note, however, that

  ** this means that the row change count will be incorrect.

  */

  if( pWhere==0 && !triggers_exist && !IsVirtual(pTab) ){

    if( db->flags & SQLITE_CountRows ){

      /* If counting rows deleted, just count the total number of

      ** entries in the table. */

      int endOfLoop = sqlite3VdbeMakeLabel(v);

      int addr2;

      if( !isView ){

        sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);

      }

      sqlite3VdbeAddOp(v, OP_Rewind, iCur, sqlite3VdbeCurrentAddr(v)+2);

      addr2 = sqlite3VdbeAddOp(v, OP_AddImm, 1, 0);

      sqlite3VdbeAddOp(v, OP_Next, iCur, addr2);

      sqlite3VdbeResolveLabel(v, endOfLoop);

      sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

    }

    if( !isView ){

      sqlite3VdbeAddOp(v, OP_Clear, pTab->tnum, iDb);

      if( !pParse->nested ){

        sqlite3VdbeChangeP3(v, -1, pTab->zName, P3_STATIC);

      }

      for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){

        assert( pIdx->pSchema==pTab->pSchema );

        sqlite3VdbeAddOp(v, OP_Clear, pIdx->tnum, iDb);

      }

    }

  } 

  /* The usual case: There is a WHERE clause so we have to scan through

  ** the table and pick which records to delete.

  */

  else{

    /* Begin the database scan

    */

    pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0);

    if( pWInfo==0 ) goto delete_from_cleanup;

    /* Remember the rowid of every item to be deleted.

    */

    sqlite3VdbeAddOp(v, IsVirtual(pTab) ? OP_VRowid : OP_Rowid, iCur, 0);

    sqlite3VdbeAddOp(v, OP_FifoWrite, 0, 0);

    if( db->flags & SQLITE_CountRows ){

      sqlite3VdbeAddOp(v, OP_AddImm, 1, 0);

    }

    /* End the database scan loop.

    */

    sqlite3WhereEnd(pWInfo);

    /* Open the pseudo-table used to store OLD if there are triggers.

    */

    if( triggers_exist ){

      sqlite3VdbeAddOp(v, OP_OpenPseudo, oldIdx, 0);

      sqlite3VdbeAddOp(v, OP_SetNumColumns, oldIdx, pTab->nCol);

    }

    /* Delete every item whose key was written to the list during the

    ** database scan.  We have to delete items after the scan is complete

    ** because deleting an item can change the scan order.

    */

    end = sqlite3VdbeMakeLabel(v);

    /* This is the beginning of the delete loop when there are

    ** row triggers.

    */

    if( triggers_exist ){

      addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, end);

      if( !isView ){

        sqlite3VdbeAddOp(v, OP_Dup, 0, 0);

        sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);

      }

      sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);

      sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);

      sqlite3VdbeAddOp(v, OP_RowData, iCur, 0);

      sqlite3VdbeAddOp(v, OP_Insert, oldIdx, 0);

      if( !isView ){

        sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

      }

      (void)sqlite3CodeRowTrigger(pParse, TK_DELETE, 0, TRIGGER_BEFORE, pTab,

          -1, oldIdx, (pParse->trigStack)?pParse->trigStack->orconf:OE_Default,

          addr);

    }

    if( !isView ){

      /* Open cursors for the table we are deleting from and all its

      ** indices.  If there are row triggers, this happens inside the

      ** OP_FifoRead loop because the cursor have to all be closed

      ** before the trigger fires.  If there are no row triggers, the

      ** cursors are opened only once on the outside the loop.

      */

      sqlite3OpenTableAndIndices(pParse, pTab, iCur, OP_OpenWrite);

      /* This is the beginning of the delete loop when there are no

      ** row triggers */

      if( !triggers_exist ){ 

        addr = sqlite3VdbeAddOp(v, OP_FifoRead, 0, end);

      }

      /* Delete the row */

#ifndef SQLITE_OMIT_VIRTUALTABLE

      if( IsVirtual(pTab) ){

        pParse->pVirtualLock = pTab;

        sqlite3VdbeOp3(v, OP_VUpdate, 0, 1, (const char*)pTab->pVtab, P3_VTAB);

      }else

#endif

      {

        sqlite3GenerateRowDelete(db, v, pTab, iCur, pParse->nested==0);

      }

    }

    /* If there are row triggers, close all cursors then invoke

    ** the AFTER triggers

    */

    if( triggers_exist ){

      if( !isView ){

        for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

          sqlite3VdbeAddOp(v, OP_Close, iCur + i, pIdx->tnum);

        }

        sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

      }

      (void)sqlite3CodeRowTrigger(pParse, TK_DELETE, 0, TRIGGER_AFTER, pTab, -1,

          oldIdx, (pParse->trigStack)?pParse->trigStack->orconf:OE_Default,

          addr);

    }

    /* End of the delete loop */

    sqlite3VdbeAddOp(v, OP_Goto, 0, addr);

    sqlite3VdbeResolveLabel(v, end);

    /* Close the cursors after the loop if there are no row triggers */

    if( !triggers_exist && !IsVirtual(pTab) ){

      for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

        sqlite3VdbeAddOp(v, OP_Close, iCur + i, pIdx->tnum);

      }

      sqlite3VdbeAddOp(v, OP_Close, iCur, 0);

    }

  }

  /*

  ** Return the number of rows that were deleted. If this routine is 

  ** generating code because of a call to sqlite3NestedParse(), do not

  ** invoke the callback function.

  */

  if( db->flags & SQLITE_CountRows && pParse->nested==0 && !pParse->trigStack ){

    sqlite3VdbeAddOp(v, OP_Callback, 1, 0);

    sqlite3VdbeSetNumCols(v, 1);

    sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows deleted", P3_STATIC);

  }

delete_from_cleanup:

  sqlite3AuthContextPop(&sContext);

  sqlite3SrcListDelete(pTabList);

  sqlite3ExprDelete(pWhere);

  return;

}

/*

** This routine generates VDBE code that causes a single row of a

** single table to be deleted.

**

** The VDBE must be in a particular state when this routine is called.

** These are the requirements:

**

**   1.  A read/write cursor pointing to pTab, the table containing the row

**       to be deleted, must be opened as cursor number "base".

**

**   2.  Read/write cursors for all indices of pTab must be open as

**       cursor number base+i for the i-th index.

**

**   3.  The record number of the row to be deleted must be on the top

**       of the stack.

**

** This routine pops the top of the stack to remove the record number

** and then generates code to remove both the table record and all index

** entries that point to that record.

*/

void sqlite3GenerateRowDelete(

  sqlite3 *db,       /* The database containing the index */

  Vdbe *v,           /* Generate code into this VDBE */

  Table *pTab,       /* Table containing the row to be deleted */

  int iCur,          /* Cursor number for the table */

  int count          /* Increment the row change counter */

){

  int addr;

  addr = sqlite3VdbeAddOp(v, OP_NotExists, iCur, 0);

  sqlite3GenerateRowIndexDelete(v, pTab, iCur, 0);

  sqlite3VdbeAddOp(v, OP_Delete, iCur, (count?OPFLAG_NCHANGE:0));

  if( count ){

    sqlite3VdbeChangeP3(v, -1, pTab->zName, P3_STATIC);

  }

  sqlite3VdbeJumpHere(v, addr);

}

/*

** This routine generates VDBE code that causes the deletion of all

** index entries associated with a single row of a single table.

**

** The VDBE must be in a particular state when this routine is called.

** These are the requirements:

**

**   1.  A read/write cursor pointing to pTab, the table containing the row

**       to be deleted, must be opened as cursor number "iCur".

**

**   2.  Read/write cursors for all indices of pTab must be open as

**       cursor number iCur+i for the i-th index.

**

**   3.  The "iCur" cursor must be pointing to the row that is to be

**       deleted.

*/

void sqlite3GenerateRowIndexDelete(

  Vdbe *v,           /* Generate code into this VDBE */

  Table *pTab,       /* Table containing the row to be deleted */

  int iCur,          /* Cursor number for the table */

  char *aIdxUsed     /* Only delete if aIdxUsed!=0 && aIdxUsed[i]!=0 */

){

  int i;

  Index *pIdx;

  for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){

    if( aIdxUsed!=0 && aIdxUsed[i-1]==0 ) continue;

    sqlite3GenerateIndexKey(v, pIdx, iCur);

    sqlite3VdbeAddOp(v, OP_IdxDelete, iCur+i, 0);

  }

}

/*

** Generate code that will assemble an index key and put it on the top

** of the tack.  The key with be for index pIdx which is an index on pTab.

** iCur is the index of a cursor open on the pTab table and pointing to

** the entry that needs indexing.

*/

void sqlite3GenerateIndexKey(

  Vdbe *v,           /* Generate code into this VDBE */

  Index *pIdx,       /* The index for which to generate a key */

  int iCur           /* Cursor number for the pIdx->pTable table */

){

  int j;

  Table *pTab = pIdx->pTable;

  sqlite3VdbeAddOp(v, OP_Rowid, iCur, 0);

  for(j=0; j<pIdx->nColumn; j++){

    int idx = pIdx->aiColumn[j];

    if( idx==pTab->iPKey ){

      sqlite3VdbeAddOp(v, OP_Dup, j, 0);

    }else{

      sqlite3VdbeAddOp(v, OP_Column, iCur, idx);

      sqlite3ColumnDefault(v, pTab, idx);

    }

  }

  sqlite3VdbeAddOp(v, OP_MakeIdxRec, pIdx->nColumn, 0);

  sqlite3IndexAffinityStr(v, pIdx);

}