**   http://www.hwaci.com/drh/
**
*************************************************************************
** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  Also found here are subroutines
** to generate VDBE code to evaluate expressions.
**
** $Id: where.c,v 1.2 2000/05/30 03:28:36 drh Exp $
*/
#include "sqliteInt.h"

/*
** The query generator uses an array of instances of this structure to
** help it analyze the subexpressions of the WHERE clause.  Each WHERE
** clause subexpression is separated from the others by an AND operator.
................................................................................
  }

  /* Figure out a good nesting order for the tables.  aOrder[0] will
  ** be the index in pTabList of the outermost table.  aOrder[1] will
  ** be the first nested loop and so on.  aOrder[pTabList->nId-1] will
  ** be the innermost loop.
  **
  ** Someday will put in a good algorithm here to reorder to the loops
  ** for an effiecient query.  But for now, just use whatever order the
  ** tables appear in in the pTabList.
  */
  for(i=0; i<pTabList->nId; i++){
    aOrder[i] = i;
  }

................................................................................
  for(i=0; i<pTabList->nId && i<ARRAYSIZE(aIdx); i++){
    int idx = aOrder[i];
    Table *pTab = pTabList->a[idx].pTab;
    Index *pIdx;
    Index *pBestIdx = 0;

    /* Do a search for usable indices.  Leave pBestIdx pointing to
    ** most specific usable index.
    **
    ** "Most specific" means that pBestIdx is the usable index that
    ** has the largest value for nField.  A usable index is one for
    ** which there are subexpressions to compute every field of the
    ** index.
    */
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
................................................................................
      if( fieldMask + 1 == (1<<pIdx->nField) ){
        if( pBestIdx==0 || pBestIdx->nField<pIdx->nField ){
          pBestIdx = pIdx;
        }
      }
    }
    aIdx[i] = pBestIdx;

  }

  /* Open all tables in the pTabList and all indices in aIdx[].
  */
  for(i=0; i<pTabList->nId; i++){
    sqliteVdbeAddOp(v, OP_Open, i, 0, pTabList->a[i].pTab->zName, 0);
    if( i<ARRAYSIZE(aIdx) && aIdx[i]!=0 ){

**   http://www.hwaci.com/drh/
**
*************************************************************************
** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  Also found here are subroutines
** to generate VDBE code to evaluate expressions.
**
** $Id: where.c,v 1.3 2000/05/30 20:17:49 drh Exp $
*/
#include "sqliteInt.h"

/*
** The query generator uses an array of instances of this structure to
** help it analyze the subexpressions of the WHERE clause.  Each WHERE
** clause subexpression is separated from the others by an AND operator.
................................................................................
  }

  /* Figure out a good nesting order for the tables.  aOrder[0] will
  ** be the index in pTabList of the outermost table.  aOrder[1] will
  ** be the first nested loop and so on.  aOrder[pTabList->nId-1] will
  ** be the innermost loop.
  **
  ** Someday will put in a good algorithm here to reorder the loops
  ** for an effiecient query.  But for now, just use whatever order the
  ** tables appear in in the pTabList.
  */
  for(i=0; i<pTabList->nId; i++){
    aOrder[i] = i;
  }

................................................................................
  for(i=0; i<pTabList->nId && i<ARRAYSIZE(aIdx); i++){
    int idx = aOrder[i];
    Table *pTab = pTabList->a[idx].pTab;
    Index *pIdx;
    Index *pBestIdx = 0;

    /* Do a search for usable indices.  Leave pBestIdx pointing to
    ** the most specific usable index.
    **
    ** "Most specific" means that pBestIdx is the usable index that
    ** has the largest value for nField.  A usable index is one for
    ** which there are subexpressions to compute every field of the
    ** index.
    */
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
................................................................................
      if( fieldMask + 1 == (1<<pIdx->nField) ){
        if( pBestIdx==0 || pBestIdx->nField<pIdx->nField ){
          pBestIdx = pIdx;
        }
      }
    }
    aIdx[i] = pBestIdx;
    loopMask |= 1<<idx;
  }

  /* Open all tables in the pTabList and all indices in aIdx[].
  */
  for(i=0; i<pTabList->nId; i++){
    sqliteVdbeAddOp(v, OP_Open, i, 0, pTabList->a[i].pTab->zName, 0);
    if( i<ARRAYSIZE(aIdx) && aIdx[i]!=0 ){