SQLite

/*
** 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.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.350 2005/01/03 01:27:19 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** These #defines should enable >2GB file support on Posix if the
** underlying operating system supports it.  If the OS lacks

** access or modified by other modules.
*/
struct WhereLevel {
  int iMem;            /* Memory cell used by this level */
  Index *pIdx;         /* Index used.  NULL if no index */
  int iTabCur;         /* The VDBE cursor used to access the table */
  int iIdxCur;         /* The VDBE cursor used to acesss pIdx */
  int score;           /* How well this index scored */
  int brk;             /* Jump here to break out of the loop */
  int cont;            /* Jump here to continue with the next loop cycle */
  int op, p1, p2;      /* Opcode used to terminate the loop */
  int iLeftJoin;       /* Memory cell used to implement LEFT OUTER JOIN */
  int top;             /* First instruction of interior of the loop */
  int inOp, inP1, inP2;/* Opcode used to implement an IN operator */
  int bRev;            /* Do the scan in the reverse direction */

** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is reponsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.125 2005/01/03 01:27:19 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.

** The number of bits in a Bitmask
*/
#define BMS  (sizeof(Bitmask)*8-1)


/*
** Generate the beginning of the loop used for WHERE clause processing.
** The return value is a pointer to an opaque structure that contains
** information needed to terminate the loop.  Later, the calling routine
** should invoke sqlite3WhereEnd() with the return value of this function
** in order to complete the WHERE clause processing.
**
** If an error occurs, this routine returns NULL.
**
** The basic idea is to do a nested loop, one loop for each table in

      continue;
    }

    /* Do a search for usable indices.  Leave pBestIdx pointing to
    ** the "best" index.  pBestIdx is left set to NULL if no indices
    ** are usable.
    **
    ** The best index is the one with the highest score.  The score
    ** for the index is determined as follows.  For each of the
    ** left-most terms that is fixed by an equality operator, add
    ** 32 to the score.  The right-most term of the index may be
    ** constrained by an inequality.  Add 4 if for an "x<..." constraint
    ** and add 8 for an "x>..." constraint.  If both constraints
    ** are present, add 12.
    **
    ** If the left-most term of the index uses an IN operator

  }

  /* The "break" point is here, just past the end of the outer loop.
  ** Set it.
  */
  sqlite3VdbeResolveLabel(v, pWInfo->iBreak);

  /* Close all of the cursors that were opend by sqlite3WhereBegin.
  */
  pLevel = pWInfo->a;
  pTabItem = pTabList->a;
  for(i=0; i<pTabList->nSrc; i++, pTabItem++, pLevel++){
    Table *pTab = pTabItem->pTab;
    assert( pTab!=0 );
    if( pTab->isTransient || pTab->pSelect ) continue;
    if( (pLevel->score & 1)==0 ){
      sqlite3VdbeAddOp(v, OP_Close, pTabItem->iCursor, 0);
    }
    if( pLevel->pIdx!=0 ){
      sqlite3VdbeAddOp(v, OP_Close, pLevel->iIdxCur, 0);
    }

    /* Make cursor substitutions for cases where we want to use
    ** just the index and never reference the table.
    ** 
    ** Calls to the code generator in between sqlite3WhereBegin and
    ** sqlite3WhereEnd will have created code that references the table
    ** directly.  This loop scans all that code looking for opcodes
    ** that reference the table and converts them into opcodes that
    ** reference the index.