SQLite

**
** If the BTREE_SAVEPOSITION bit of the flags parameter is zero, then
** the cursor is left pointing at an arbitrary location after the delete.
** But if that bit is set, then the cursor is left in a state such that
** the next call to BtreeNext() or BtreePrev() moves it to the same row
** as it would have been on if the call to BtreeDelete() had been omitted.
**
** The BTREE_IDXDELETE bit of flags indicates that this is a delete of
** an index entry where the corresponding table row has already been deleted.
** The BTREE_IDXDELETE bit is a hint that is not used by this implementation,
** The BTREE_AUXDELETE bit of flags indicates that is one of several deletes
** associated with a single table entry and its indexes.  Only one of those
** deletes is considered the "primary" delete.  The primary delete occurs
** on a cursor that is not a BTREE_FORDELETE cursor.  All but one delete
** operation on non-FORDELETE cursors is tagged with the AUXDELETE flag.
** The BTREE_AUXDELETE bit is a hint that is not used by this implementation,
** but which might be used by alternative storage engines.
*/
int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;              
  int rc;                              /* Return code */
  MemPage *pPage;                      /* Page to delete cell from */

  assert( pBt->inTransaction==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( pCur->curFlags & BTCF_WriteFlag );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );
  assert( !hasReadConflicts(p, pCur->pgnoRoot) );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  assert( pCur->eState==CURSOR_VALID );
  assert( (flags & ~(BTREE_SAVEPOSITION | BTREE_IDXDELETE))==0 );
  assert( (flags & ~(BTREE_SAVEPOSITION | BTREE_AUXDELETE))==0 );

  iCellDepth = pCur->iPage;
  iCellIdx = pCur->aiIdx[iCellDepth];
  pPage = pCur->apPage[iCellDepth];
  pCell = findCell(pPage, iCellIdx);

  /* If the page containing the entry to delete is not a leaf page, move

);
int sqlite3BtreeCursorHasMoved(BtCursor*);
int sqlite3BtreeCursorRestore(BtCursor*, int*);
int sqlite3BtreeDelete(BtCursor*, u8 flags);

/* Allowed flags for the 2nd argument to sqlite3BtreeDelete() */
#define BTREE_SAVEPOSITION 0x02  /* Leave cursor pointing at NEXT or PREV */
#define BTREE_IDXDELETE    0x04  /* this is index, table row already deleted */
#define BTREE_AUXDELETE    0x04  /* not the primary delete operation */

int sqlite3BtreeInsert(BtCursor*, const void *pKey, i64 nKey,
                                  const void *pData, int nData,
                                  int nZero, int bias, int seekResult);
int sqlite3BtreeFirst(BtCursor*, int *pRes);
int sqlite3BtreeLast(BtCursor*, int *pRes);
int sqlite3BtreeNext(BtCursor*, int *pRes);

    u8 p5 = 0;
    sqlite3GenerateRowIndexDelete(pParse, pTab, iDataCur, iIdxCur,0,iIdxNoSeek);
    sqlite3VdbeAddOp2(v, OP_Delete, iDataCur, (count?OPFLAG_NCHANGE:0));
    if( count ){
      sqlite3VdbeChangeP4(v, -1, pTab->zName, P4_TRANSIENT);
    }
    if( eMode!=ONEPASS_OFF ){
      sqlite3VdbeChangeP5(v, OPFLAG_IDXDELETE);
      sqlite3VdbeChangeP5(v, OPFLAG_AUXDELETE);
      p5 = OPFLAG_IDXDELETE;
    }
    if( iIdxNoSeek>=0 ){
      sqlite3VdbeAddOp1(v, OP_Delete, iIdxNoSeek);
      p5 = 0;
    }
    if( eMode==ONEPASS_MULTI ) p5 |= OPFLAG_SAVEPOSITION;
    sqlite3VdbeChangeP5(v, p5);
  }

  /* Do any ON CASCADE, SET NULL or SET DEFAULT operations required to
  ** handle rows (possibly in other tables) that refer via a foreign key

#define OPFLAG_TYPEOFARG     0x80    /* OP_Column only used for typeof() */
#define OPFLAG_BULKCSR       0x01    /* OP_Open** used to open bulk cursor */
#define OPFLAG_SEEKEQ        0x02    /* OP_Open** cursor uses EQ seek only */
#define OPFLAG_FORDELETE     0x08    /* OP_Open should use BTREE_FORDELETE */
#define OPFLAG_P2ISREG       0x10    /* P2 to OP_Open** is a register number */
#define OPFLAG_PERMUTE       0x01    /* OP_Compare: use the permutation */
#define OPFLAG_SAVEPOSITION  0x02    /* OP_Delete: keep cursor position */
#define OPFLAG_IDXDELETE     0x04    /* OP_Delete: index in a DELETE op */
#define OPFLAG_AUXDELETE     0x04    /* OP_Delete: index in a DELETE op */

/*
 * Each trigger present in the database schema is stored as an instance of
 * struct Trigger. 
 *
 * Pointers to instances of struct Trigger are stored in two ways.
 * 1. In the "trigHash" hash table (part of the sqlite3* that represents the 

){
  Op *aOp = p->aOp;          /* Copy of p->aOp */
  Op *pOp = aOp;             /* Current operation */
#if defined(SQLITE_DEBUG) || defined(VDBE_PROFILE)
  Op *pOrigOp;               /* Value of pOp at the top of the loop */
#endif
#ifdef SQLITE_DEBUG
  int nExtraDelete = 0;      /* Verifies FORDELETE and IDXDELETE flags */
  int nExtraDelete = 0;      /* Verifies FORDELETE and AUXDELETE flags */
#endif
  int rc = SQLITE_OK;        /* Value to return */
  sqlite3 *db = p->db;       /* The database */
  u8 resetSchemaOnFault = 0; /* Reset schema after an error if positive */
  u8 encoding = ENC(db);     /* The database encoding */
  int iCompare = 0;          /* Result of last OP_Compare operation */
  unsigned nVmStep = 0;      /* Number of virtual machine steps */

** the cursor will be left pointing at  either the next or the previous
** record in the table. If it is left pointing at the next record, then
** the next Next instruction will be a no-op. As a result, in this case
** it is ok to delete a record from within a Next loop. If 
** OPFLAG_SAVEPOSITION bit of P5 is clear, then the cursor will be
** left in an undefined state.
**
** If the OPFLAG_IDXDELETE bit is set on P5, that indicates that this
** delete is on an index cursor where the corresponding table row has
** already been deleted.
** If the OPFLAG_AUXDELETE bit is set on P5, that indicates that this
** delete one of several associated with deleting a table row and all its
** associated index entries.  Exactly one of those deletes is the "primary"
** delete.  The others are all on OPFLAG_FORDELETE cursors or else are
** marked with the AUXDELETE flag.
**
** If the OPFLAG_NCHANGE flag of P2 (NB: P2 not P5) is set, then the row
** change count is incremented (otherwise not).
**
** P1 must not be pseudo-table.  It has to be a real table with
** multiple rows.
**

  if( pOp->p4.z && pC->isTable && pOp->p5==0 ){
    i64 iKey = 0;
    sqlite3BtreeKeySize(pC->uc.pCursor, &iKey);
    assert( pC->movetoTarget==iKey ); 
  }
#endif

  /* Only flags that can be set are SAVEPOISTION and IDXDELETE */ 
  assert( (pOp->p5 & ~(OPFLAG_SAVEPOSITION|OPFLAG_IDXDELETE))==0 );
  /* Only flags that can be set are SAVEPOISTION and AUXDELETE */ 
  assert( (pOp->p5 & ~(OPFLAG_SAVEPOSITION|OPFLAG_AUXDELETE))==0 );
  assert( OPFLAG_SAVEPOSITION==BTREE_SAVEPOSITION );
  assert( OPFLAG_IDXDELETE==BTREE_IDXDELETE );
  assert( OPFLAG_AUXDELETE==BTREE_AUXDELETE );

#ifdef SQLITE_DEBUG
  if( pC->isEphemeral==0
   && (pOp->p5 & OPFLAG_IDXDELETE)==0
   && (pOp->p5 & OPFLAG_AUXDELETE)==0
   && (pC->wrFlag & OPFLAG_FORDELETE)==0
  ){
    nExtraDelete++;
  }
  if( pOp->p2 & OPFLAG_NCHANGE ){
    nExtraDelete--;
  }

  r.default_rc = 0;
  r.aMem = &aMem[pOp->p2];
#ifdef SQLITE_DEBUG
  {
    int i;
    for(i=0; i<r.nField; i++) assert( memIsValid(&r.aMem[i]) );
    if( pC->isEphemeral==0
     && (pOp->p5 & OPFLAG_IDXDELETE)==0
     && (pOp->p5 & OPFLAG_AUXDELETE)==0
     && (pC->wrFlag & OPFLAG_FORDELETE)==0
    ){
      nExtraDelete++;
    }
  }
#endif
  rc = sqlite3BtreeMovetoUnpacked(pCrsr, &r, 0, 0, &res);