src/delete.c

/*
** 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 1.207 2009/08/08 18:01:08 drh 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){
  struct SrcList_item *pItem = pSrc->a;
  Table *pTab;
  assert( pItem && pSrc->nSrc==1 );
  pTab = sqlite3LocateTable(pParse, 0, pItem->zName, pItem->zDatabase);
  sqlite3DeleteTable(pItem->pTab);
  pItem->pTab = pTab;
  if( pTab ){
    pTab->nRef++;
  }
  if( sqlite3IndexedByLookup(pParse, pItem) ){
    pTab = 0;
  }
  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){
  /* A table is not writable under the following circumstances:
  **
  **   1) It is a virtual table and no implementation of the xUpdate method
  **      has been provided, or
  **   2) It is a system table (i.e. sqlite_master), this call is not
  **      part of a nested parse and writable_schema pragma has not 
  **      been specified.
  **
  ** In either case leave an error message in pParse and return non-zero.
  */
  if( ( IsVirtual(pTab) 
     && sqlite3GetVTable(pParse->db, pTab)->pMod->pModule->xUpdate==0 )
   || ( (pTab->tabFlags & TF_Readonly)!=0
     && (pParse->db->flags & SQLITE_WriteSchema)==0
     && pParse->nested==0 )
  ){
    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;
}


#if !defined(SQLITE_OMIT_VIEW) && !defined(SQLITE_OMIT_TRIGGER)
/*
** Evaluate a view and store its result in an ephemeral table.  The
** pWhere argument is an optional WHERE clause that restricts the
** set of rows in the view that are to be added to the ephemeral table.
*/
void sqlite3MaterializeView(
  Parse *pParse,       /* Parsing context */
  Table *pView,        /* View definition */
  Expr *pWhere,        /* Optional WHERE clause to be added */
  int iCur             /* Cursor number for ephemerial table */
){
  SelectDest dest;
  Select *pDup;
  sqlite3 *db = pParse->db;

  pDup = sqlite3SelectDup(db, pView->pSelect, 0);
  if( pWhere ){
    SrcList *pFrom;
    
    pWhere = sqlite3ExprDup(db, pWhere, 0);
    pFrom = sqlite3SrcListAppend(db, 0, 0, 0);
    if( pFrom ){
      assert( pFrom->nSrc==1 );
      pFrom->a[0].zAlias = sqlite3DbStrDup(db, pView->zName);
      pFrom->a[0].pSelect = pDup;
      assert( pFrom->a[0].pOn==0 );
      assert( pFrom->a[0].pUsing==0 );
    }else{
      sqlite3SelectDelete(db, pDup);
    }
    pDup = sqlite3SelectNew(pParse, 0, pFrom, pWhere, 0, 0, 0, 0, 0, 0);
  }
  sqlite3SelectDestInit(&dest, SRT_EphemTab, iCur);
  sqlite3Select(pParse, pDup, &dest);
  sqlite3SelectDelete(db, pDup);
}
#endif /* !defined(SQLITE_OMIT_VIEW) && !defined(SQLITE_OMIT_TRIGGER) */

#if defined(SQLITE_ENABLE_UPDATE_DELETE_LIMIT) && !defined(SQLITE_OMIT_SUBQUERY)
/*
** Generate an expression tree to implement the WHERE, ORDER BY,
** and LIMIT/OFFSET portion of DELETE and UPDATE statements.
**
**     DELETE FROM table_wxyz WHERE a<5 ORDER BY a LIMIT 1;
**                            \__________________________/
**                               pLimitWhere (pInClause)
*/
Expr *sqlite3LimitWhere(
  Parse *pParse,               /* The parser context */
  SrcList *pSrc,               /* the FROM clause -- which tables to scan */
  Expr *pWhere,                /* The WHERE clause.  May be null */
  ExprList *pOrderBy,          /* The ORDER BY clause.  May be null */
  Expr *pLimit,                /* The LIMIT clause.  May be null */
  Expr *pOffset,               /* The OFFSET clause.  May be null */
  char *zStmtType              /* Either DELETE or UPDATE.  For error messages. */
){
  Expr *pWhereRowid = NULL;    /* WHERE rowid .. */
  Expr *pInClause = NULL;      /* WHERE rowid IN ( select ) */
  Expr *pSelectRowid = NULL;   /* SELECT rowid ... */
  ExprList *pEList = NULL;     /* Expression list contaning only pSelectRowid */
  SrcList *pSelectSrc = NULL;  /* SELECT rowid FROM x ... (dup of pSrc) */
  Select *pSelect = NULL;      /* Complete SELECT tree */

  /* Check that there isn't an ORDER BY without a LIMIT clause.
  */
  if( pOrderBy && (pLimit == 0) ) {
    sqlite3ErrorMsg(pParse, "ORDER BY without LIMIT on %s", zStmtType);
    pParse->parseError = 1;
    goto limit_where_cleanup_2;
  }

  /* We only need to generate a select expression if there
  ** is a limit/offset term to enforce.
  */
  if( pLimit == 0 ) {
    /* if pLimit is null, pOffset will always be null as well. */
    assert( pOffset == 0 );
    return pWhere;
  }

  /* Generate a select expression tree to enforce the limit/offset 
  ** term for the DELETE or UPDATE statement.  For example:
  **   DELETE FROM table_a WHERE col1=1 ORDER BY col2 LIMIT 1 OFFSET 1
  ** becomes:
  **   DELETE FROM table_a WHERE rowid IN ( 
  **     SELECT rowid FROM table_a WHERE col1=1 ORDER BY col2 LIMIT 1 OFFSET 1
  **   );
  */

  pSelectRowid = sqlite3PExpr(pParse, TK_ROW, 0, 0, 0);
  if( pSelectRowid == 0 ) goto limit_where_cleanup_2;
  pEList = sqlite3ExprListAppend(pParse, 0, pSelectRowid);
  if( pEList == 0 ) goto limit_where_cleanup_2;

  /* duplicate the FROM clause as it is needed by both the DELETE/UPDATE tree
  ** and the SELECT subtree. */
  pSelectSrc = sqlite3SrcListDup(pParse->db, pSrc, 0);
  if( pSelectSrc == 0 ) {
    sqlite3ExprListDelete(pParse->db, pEList);
    goto limit_where_cleanup_2;
  }

  /* generate the SELECT expression tree. */
  pSelect = sqlite3SelectNew(pParse,pEList,pSelectSrc,pWhere,0,0,
                             pOrderBy,0,pLimit,pOffset);
  if( pSelect == 0 ) return 0;

  /* now generate the new WHERE rowid IN clause for the DELETE/UDPATE */
  pWhereRowid = sqlite3PExpr(pParse, TK_ROW, 0, 0, 0);
  if( pWhereRowid == 0 ) goto limit_where_cleanup_1;
  pInClause = sqlite3PExpr(pParse, TK_IN, pWhereRowid, 0, 0);
  if( pInClause == 0 ) goto limit_where_cleanup_1;

  pInClause->x.pSelect = pSelect;
  pInClause->flags |= EP_xIsSelect;
  sqlite3ExprSetHeight(pParse, pInClause);
  return pInClause;

  /* something went wrong. clean up anything allocated. */
limit_where_cleanup_1:
  sqlite3SelectDelete(pParse->db, pSelect);
  return 0;

limit_where_cleanup_2:
  sqlite3ExprDelete(pParse->db, pWhere);
  sqlite3ExprListDelete(pParse->db, pOrderBy);
  sqlite3ExprDelete(pParse->db, pLimit);
  sqlite3ExprDelete(pParse->db, pOffset);
  return 0;
}
#endif /* defined(SQLITE_ENABLE_UPDATE_DELETE_LIMIT) && !defined(SQLITE_OMIT_SUBQUERY) */

/*
** 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 */
  NameContext sNC;       /* Name context to resolve expressions in */
  int iDb;               /* Database number */
  int memCnt = -1;       /* Memory cell used for change counting */
  int rcauth;            /* Value returned by authorization callback */

#ifndef SQLITE_OMIT_TRIGGER
  int isView;                  /* True if attempting to delete from a view */
  Trigger *pTrigger;           /* List of table triggers, if required */
#endif

  memset(&sContext, 0, sizeof(sContext));
  db = pParse->db;
  if( pParse->nErr || db->mallocFailed ){
    goto delete_from_cleanup;
  }
  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
  pTrigger = sqlite3TriggersExist(pParse, pTab, TK_DELETE, 0, 0);
  isView = pTab->pSelect!=0;
#else
# define pTrigger 0
# define isView 0
#endif
#ifdef SQLITE_OMIT_VIEW
# undef isView
# define isView 0
#endif

  /* If pTab is really a view, make sure it has been initialized.
  */
  if( sqlite3ViewGetColumnNames(pParse, pTab) ){
    goto delete_from_cleanup;
  }

  if( sqlite3IsReadOnly(pParse, pTab, (pTrigger?1:0)) ){
    goto delete_from_cleanup;
  }
  iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
  assert( iDb<db->nDb );
  zDb = db->aDb[iDb].zName;
  rcauth = sqlite3AuthCheck(pParse, SQLITE_DELETE, pTab->zName, 0, zDb);
  assert( rcauth==SQLITE_OK || rcauth==SQLITE_DENY || rcauth==SQLITE_IGNORE );
  if( rcauth==SQLITE_DENY ){
    goto delete_from_cleanup;
  }
  assert(!isView || pTrigger);

  /* Assign  cursor number to the table and all its indices.
  */
  assert( pTabList->nSrc==1 );
  iCur = pTabList->a[0].iCursor = pParse->nTab++;
  for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
    pParse->nTab++;
  }

  /* 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, (pTrigger?1:0), iDb);

  /* If we are trying to delete from a view, realize that view into
  ** a ephemeral table.
  */
#if !defined(SQLITE_OMIT_VIEW) && !defined(SQLITE_OMIT_TRIGGER)
  if( isView ){
    sqlite3MaterializeView(pParse, pTab, pWhere, iCur);
  }
#endif

  /* Resolve the column names in the WHERE clause.
  */
  memset(&sNC, 0, sizeof(sNC));
  sNC.pParse = pParse;
  sNC.pSrcList = pTabList;
  if( sqlite3ResolveExprNames(&sNC, pWhere) ){
    goto delete_from_cleanup;
  }

  /* Initialize the counter of the number of rows deleted, if
  ** we are counting rows.
  */
  if( db->flags & SQLITE_CountRows ){
    memCnt = ++pParse->nMem;
    sqlite3VdbeAddOp2(v, OP_Integer, 0, memCnt);
  }

#ifndef SQLITE_OMIT_TRUNCATE_OPTIMIZATION
  /* 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( rcauth==SQLITE_OK && pWhere==0 && !pTrigger && !IsVirtual(pTab) ){
    assert( !isView );
    sqlite3VdbeAddOp4(v, OP_Clear, pTab->tnum, iDb, memCnt,
                      pTab->zName, P4_STATIC);
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
      assert( pIdx->pSchema==pTab->pSchema );
      sqlite3VdbeAddOp2(v, OP_Clear, pIdx->tnum, iDb);
    }
  }else
#endif /* SQLITE_OMIT_TRUNCATE_OPTIMIZATION */
  /* The usual case: There is a WHERE clause so we have to scan through
  ** the table and pick which records to delete.
  */
  {
    int iRowSet = ++pParse->nMem;   /* Register for rowset of rows to delete */
    int iRowid = ++pParse->nMem;    /* Used for storing rowid values. */
    int regOld = pParse->nMem + 1;  /* Start of array for old.* (if triggers) */
    int regRowid;                   /* Actual register containing rowids */

    /* Collect rowids of every row to be deleted.
    */
    sqlite3VdbeAddOp2(v, OP_Null, 0, iRowSet);
    pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere,0,WHERE_DUPLICATES_OK);
    if( pWInfo==0 ) goto delete_from_cleanup;
    regRowid = sqlite3ExprCodeGetColumn(pParse, pTab, -1, iCur, iRowid, 0);
    sqlite3VdbeAddOp2(v, OP_RowSetAdd, iRowSet, regRowid);
    if( db->flags & SQLITE_CountRows ){
      sqlite3VdbeAddOp2(v, OP_AddImm, memCnt, 1);
    }
    sqlite3WhereEnd(pWInfo);

    /* 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);

    /* Unless this is a view, open cursors for the table we are 
    ** deleting from and all its indices. If this is a view, then the
    ** only effect this statement has is to fire the INSTEAD OF 
    ** triggers.  */
    if( !isView ){
      sqlite3OpenTableAndIndices(pParse, pTab, iCur, OP_OpenWrite);
    }

    addr = sqlite3VdbeAddOp3(v, OP_RowSetRead, iRowSet, end, iRowid);

    /* If there are triggers, populate an array of registers with the
    ** data required by the old.* references in the trigger bodies.  */
    if( pTrigger ){
      u32 mask = 0;         /* Mask of OLD.* columns in use */
      u32 dummy = 0;        /* Unused. Initialized to prevent valgrind error. */
      pParse->nMem += pTab->nCol;

      /* Open the pseudo-table used to store OLD if there are triggers. */
      sqlite3TriggerUses(
          pParse, pTrigger, TK_DELETE, 0, pTab, OE_Default, &mask, &dummy);

      /* If the record is no longer present in the table, jump to the
      ** next iteration of the loop through the contents of the fifo.
      */
      sqlite3VdbeAddOp3(v, OP_NotExists, iCur, addr, iRowid);

      /* Populate the OLD.* pseudo-table */
      assert( regOld==iRowid+1 );
      for(i=0; i<pTab->nCol; i++){
        if( mask==0xffffffff || mask&(1<<i) ){
          sqlite3VdbeAddOp3(v, OP_Column, iCur, i, regOld+i);
        }
      }

      sqlite3CodeRowTrigger(pParse, pTrigger, 
          TK_DELETE, 0, TRIGGER_BEFORE, pTab, -1, regOld, OE_Default, addr
      );
    }

    if( !isView ){
      /* Delete the row */
#ifndef SQLITE_OMIT_VIRTUALTABLE
      if( IsVirtual(pTab) ){
        const char *pVTab = (const char *)sqlite3GetVTable(db, pTab);
        sqlite3VtabMakeWritable(pParse, pTab);
        sqlite3VdbeAddOp4(v, OP_VUpdate, 0, 1, iRowid, pVTab, P4_VTAB);
      }else
#endif
      {
        sqlite3GenerateRowDelete(pParse, pTab, iCur, iRowid, pParse->nested==0);
      }
    }

    /* Code the AFTER triggers. This is a no-op if there are no triggers. */
    sqlite3CodeRowTrigger(pParse, 
      pTrigger, TK_DELETE, 0, TRIGGER_AFTER, pTab, -1, regOld, OE_Default, addr
    );

    /* End of the delete loop */
    sqlite3VdbeAddOp2(v, OP_Goto, 0, addr);
    sqlite3VdbeResolveLabel(v, end);

    /* Close the cursors open on the table and its indexes. */
    if( !isView && !IsVirtual(pTab) ){
      for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){
        sqlite3VdbeAddOp2(v, OP_Close, iCur + i, pIdx->tnum);
      }
      sqlite3VdbeAddOp1(v, OP_Close, iCur);
    }
  }

  /* Update the sqlite_sequence table by storing the content of the
  ** maximum rowid counter values recorded while inserting into
  ** autoincrement tables.
  */
  if( pParse->nested==0 && pParse->pTriggerTab==0 ){
    sqlite3AutoincrementEnd(pParse);
  }

  /*
  ** 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 && !pParse->pTriggerTab ){
    sqlite3VdbeAddOp2(v, OP_ResultRow, memCnt, 1);
    sqlite3VdbeSetNumCols(v, 1);
    sqlite3VdbeSetColName(v, 0, COLNAME_NAME, "rows deleted", SQLITE_STATIC);
  }

delete_from_cleanup:
  sqlite3AuthContextPop(&sContext);
  sqlite3SrcListDelete(db, pTabList);
  sqlite3ExprDelete(db, 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 stored in
**       memory cell iRowid.
**
** 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(
  Parse *pParse,     /* Parsing context */
  Table *pTab,       /* Table containing the row to be deleted */
  int iCur,          /* Cursor number for the table */
  int iRowid,        /* Memory cell that contains the rowid to delete */
  int count          /* Increment the row change counter */
){
  int addr;
  Vdbe *v;

  v = pParse->pVdbe;
  addr = sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, iRowid);
  sqlite3GenerateRowIndexDelete(pParse, pTab, iCur, 0);
  sqlite3VdbeAddOp2(v, OP_Delete, iCur, (count?OPFLAG_NCHANGE:0));
  if( count ){
    sqlite3VdbeChangeP4(v, -1, pTab->zName, P4_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(
  Parse *pParse,     /* Parsing and code generating context */
  Table *pTab,       /* Table containing the row to be deleted */
  int iCur,          /* Cursor number for the table */
  int *aRegIdx       /* Only delete if aRegIdx!=0 && aRegIdx[i]>0 */
){
  int i;
  Index *pIdx;
  int r1;

  for(i=1, pIdx=pTab->pIndex; pIdx; i++, pIdx=pIdx->pNext){
    if( aRegIdx!=0 && aRegIdx[i-1]==0 ) continue;
    r1 = sqlite3GenerateIndexKey(pParse, pIdx, iCur, 0, 0);
    sqlite3VdbeAddOp3(pParse->pVdbe, OP_IdxDelete, iCur+i, r1,pIdx->nColumn+1);
  }
}

/*
** Generate code that will assemble an index key and put it in register
** regOut.  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.
**
** Return a register number which is the first in a block of
** registers that holds the elements of the index key.  The
** block of registers has already been deallocated by the time
** this routine returns.
*/
int sqlite3GenerateIndexKey(
  Parse *pParse,     /* Parsing context */
  Index *pIdx,       /* The index for which to generate a key */
  int iCur,          /* Cursor number for the pIdx->pTable table */
  int regOut,        /* Write the new index key to this register */
  int doMakeRec      /* Run the OP_MakeRecord instruction if true */
){
  Vdbe *v = pParse->pVdbe;
  int j;
  Table *pTab = pIdx->pTable;
  int regBase;
  int nCol;

  nCol = pIdx->nColumn;
  regBase = sqlite3GetTempRange(pParse, nCol+1);
  sqlite3VdbeAddOp2(v, OP_Rowid, iCur, regBase+nCol);
  for(j=0; j<nCol; j++){
    int idx = pIdx->aiColumn[j];
    if( idx==pTab->iPKey ){
      sqlite3VdbeAddOp2(v, OP_SCopy, regBase+nCol, regBase+j);
    }else{
      sqlite3VdbeAddOp3(v, OP_Column, iCur, idx, regBase+j);
      sqlite3ColumnDefault(v, pTab, idx, -1);
    }
  }
  if( doMakeRec ){
    sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase, nCol+1, regOut);
    sqlite3VdbeChangeP4(v, -1, sqlite3IndexAffinityStr(v, pIdx), 0);
    sqlite3ExprCacheAffinityChange(pParse, regBase, nCol+1);
  }
  sqlite3ReleaseTempRange(pParse, regBase, nCol+1);
  return regBase;
}

/* Make sure "isView" gets undefined in case this file becomes part of
** the amalgamation - so that subsequent files do not see isView as a
** macro. */
#undef isView