SQLite

/*
** Create a new cursor for the BTree whose root is on the page
** iTable. If a read-only cursor is requested, it is assumed that
** the caller already has at least a read-only transaction open
** on the database already. If a write-cursor is requested, then
** the caller is assumed to have an open write transaction.
**
** If the BTREE_WRCSR bit of wrFlag is clear, then the cursor can only
** be used for reading.  If the BTREE_WRCSR bit is set, then the cursor
** can be used for reading or for writing if other conditions for writing
** are also met.  These are the conditions that must be met in order
** for writing to be allowed:
**
** 1:  The cursor must have been opened with wrFlag containing BTREE_WRCSR
**
** 2:  Other database connections that share the same pager cache
**     but which are not in the READ_UNCOMMITTED state may not have
**     cursors open with wrFlag==0 on the same table.  Otherwise
**     the changes made by this write cursor would be visible to
**     the read cursors in the other database connection.
**
** 3:  The database must be writable (not on read-only media)
**
** 4:  There must be an active transaction.
**
** The BTREE_FORDELETE bit of wrFlag may optionally be set if BTREE_WRCSR
** is set.  If FORDELETE is set, that is a hint to the implementation that
** this cursor will only be used to seek to and delete entries of an index
** as part of a larger DELETE statement.  The FORDELETE hint is not used by
** this implementation.  But in a hypothetical alternative storage engine 
** in which index entries are automatically deleted when corresponding table
** rows are deleted, the FORDELETE flag is a hint that all SEEK and DELETE
** operations on this cursor can be no-ops and all READ operations can 
** return a null row (2-bytes: 0x01 0x00).
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.
**
** It is assumed that the sqlite3BtreeCursorZero() has been called
** on pCur to initialize the memory space prior to invoking this routine.

end_insert:
  return rc;
}

/*
** Delete the entry that the cursor is pointing to. 
**
** 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,
** 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 */
  unsigned char *pCell;                /* Pointer to cell to delete */
  int iCellIdx;                        /* Index of cell to delete */
  int iCellDepth;                      /* Depth of node containing pCell */ 
  u16 szCell;                          /* Size of the cell being deleted */
  int bSkipnext = 0;                   /* Leaf cursor in SKIPNEXT state */
  u8 bPreserve = flags & BTREE_SAVEPOSITION;  /* Keep cursor valid */

  assert( cursorOwnsBtShared(pCur) );
  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 );

  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

  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,
  int *pRes
);
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 */

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);
int sqlite3BtreeEof(BtCursor*);

    sqlite3FkCheck(pParse, pTab, iOld, 0, 0, 0);
  }

  /* Delete the index and table entries. Skip this step if pTab is really
  ** a view (in which case the only effect of the DELETE statement is to
  ** fire the INSTEAD OF triggers).  */ 
  if( pTab->pSelect==0 ){
    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( iIdxNoSeek>=0 ){
      sqlite3VdbeAddOp1(v, OP_Delete, iIdxNoSeek);
      if( eMode!=ONEPASS_OFF ) p5 = OPFLAG_IDXDELETE;
    }
    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
  ** to the row just deleted. */ 
  sqlite3FkActions(pParse, pTab, 0, iOld, 0, 0);

  const char *zAuthContext;   /* Put saved Parse.zAuthContext here */
  Parse *pParse;              /* The Parse structure */
};

/*
** Bitfield flags for P5 value in various opcodes.
*/
#define OPFLAG_NCHANGE       0x01    /* OP_Insert: Set to update db->nChange */
                                     /* Also used in P2 (not P5) of OP_Delete */
#define OPFLAG_EPHEM         0x01    /* OP_Column: Ephemeral output is ok */
#define OPFLAG_LASTROWID     0x02    /* Set to update db->lastRowid */
#define OPFLAG_ISUPDATE      0x04    /* This OP_Insert is an sql UPDATE */
#define OPFLAG_APPEND        0x08    /* This is likely to be an append */
#define OPFLAG_USESEEKRESULT 0x10    /* Try to avoid a seek in BtreeInsert() */
#define OPFLAG_LENGTHARG     0x40    /* OP_Column only used for length() */
#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 */

/*
 * 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 

  break;
}

/* Opcode: Delete P1 P2 * P4 P5
**
** Delete the record at which the P1 cursor is currently pointing.
**
** If the OPFLAG_SAVEPOSITION bit of the P5 parameter is set, then
** 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_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 P4 is not NULL, then it is the name of the table that P1 is
** pointing to.  The update hook will be invoked, if it exists.
** If P4 is not NULL then the P1 cursor must have been positioned

  if( pOp->p4.z && pC->isTable && pOp->p5==0 ){
    i64 iKey = 0;
    sqlite3BtreeKeySize(pC->uc.pCursor, &iKey);
    assert( pC->movetoTarget==iKey ); 
  }
#endif
 
  assert( (pOp->p5 & ~(OPFLAG_SAVEPOSITION|OPFLAG_IDXDELETE))==0 );
  assert( OPFLAG_SAVEPOSITION==BTREE_SAVEPOSITION );
  assert( OPFLAG_IDXDELETE==BTREE_IDXDELETE );
  rc = sqlite3BtreeDelete(pC->uc.pCursor, pOp->p5);
  pC->cacheStatus = CACHE_STALE;

  /* Invoke the update-hook if required. */
  if( rc==SQLITE_OK && hasUpdateCallback ){
    db->xUpdateCallback(db->pUpdateArg, SQLITE_DELETE,
                        db->aDb[pC->iDb].zName, pOp->p4.z, pC->movetoTarget);