SQLite

**    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
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.274 2005/09/20 13:55:18 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.

        if( j<pGroupBy->nExpr-1 ){
          sqlite3VdbeAddOp(v, OP_MemLoad, iBMem+j, 0);
        }
        sqlite3VdbeAddOp(v, OP_MemLoad, iAMem+j, 0);
        if( j==0 ){
          sqlite3VdbeAddOp(v, OP_Eq, 0x200, addrProcessRow);
        }else{
          sqlite3VdbeAddOp(v, OP_Ne, 0x200, addrGroupByChange);
        }
        sqlite3VdbeChangeP3(v, -1, (void*)pKeyInfo->aColl[j], P3_COLLSEQ);
      }

      /* Generate code that runs whenever the GROUP BY changes.
      ** Change in the GROUP BY are detected by the previous code
      ** block.  If there were no changes, this block is skipped.

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.490 2005/09/20 13:55:18 drh Exp $
*/
#include "sqliteInt.h"
#include "os.h"
#include <ctype.h>
#include "vdbeInt.h"

/*

/* Opcode: Eq P1 P2 P3
**
** Pop the top two elements from the stack.  If they are equal, then
** jump to instruction P2.  Otherwise, continue to the next instruction.
**
** If the 0x100 bit of P1 is true and either operand is NULL then take the
** jump.  If the 0x100 bit of P1 is clear then fall thru if either operand
** is NULL.
**
** If the 0x200 bit of P1 is set and either operand is NULL then

** both operands are converted to integers prior to comparison.
** NULL operands are converted to zero and non-NULL operands are
** converted to 1.  Thus, for example, with 0x200 set,  NULL==NULL is true
** whereas it would normally be NULL.  Similarly,  NULL==123 is false when
** 0x200 is set but is NULL when the 0x200 bit of P1 is clear.
**
** The least significant byte of P1 (mask 0xff) must be an affinity character -
** 'n', 't', 'i' or 'o' - or 0x00. An attempt is made to coerce both values
** according to the affinity before the comparison is made. If the byte is
** 0x00, then numeric affinity is used.
**
** Once any conversions have taken place, and neither value is NULL, 

  flags = pTos->flags|pNos->flags;

  /* If either value is a NULL P2 is not zero, take the jump if the least
  ** significant byte of P1 is true. If P2 is zero, then push a NULL onto
  ** the stack.
  */
  if( flags&MEM_Null ){
    if( (pOp->p1 & 0x200)!=0 ){
      /* The 0x200 bit of P1 means, roughly "do not treat NULL as the
      ** magic SQL value it normally is - treat it as if it were another
      ** integer".
      **
      ** With 0x200 set, if either operand is NULL then both operands
      ** are converted to integers prior to being passed down into the
      ** normal comparison logic below.  NULL operands are converted to
      ** zero and non-NULL operands are converted to 1.  Thus, for example,
      ** with 0x200 set,  NULL==NULL is true whereas it would normally
      ** be NULL.  Similarly,  NULL!=123 is true.
      */
      sqlite3VdbeMemSetInt64(pTos, (pTos->flags & MEM_Null)==0);
      sqlite3VdbeMemSetInt64(pNos, (pNos->flags & MEM_Null)==0);
    }else{
      /* If the 0x200 bit of P1 is clear and either operand is NULL then
      ** the result is always NULL.  The jump is taken if the 0x100 bit
      ** of P1 is set.
      */
      popStack(&pTos, 2);
      if( pOp->p2 ){
        if( pOp->p1 & 0x100 ){
          pc = pOp->p2-1;
        }