SQLite

** 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 1.158 2005/07/29 19:43:58 drh Exp $
*/
#include "sqliteInt.h"

/*
** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
*/
#define BMS  (sizeof(Bitmask)*8)

#define WHERE_COLUMN_RANGE   0x0020   /* x<EXPR and/or x>EXPR */
#define WHERE_COLUMN_IN      0x0040   /* x IN (...) */
#define WHERE_TOP_LIMIT      0x0100   /* x<EXPR or x<=EXPR constraint */
#define WHERE_BTM_LIMIT      0x0200   /* x>EXPR or x>=EXPR constraint */
#define WHERE_IDX_ONLY       0x0800   /* Use index only - omit table */
#define WHERE_ORDERBY        0x1000   /* Output will appear in correct order */
#define WHERE_REVERSE        0x2000   /* Scan in reverse order */
#define WHERE_UNIQUE         0x4000   /* Selects no more than one row */

/*
** Initialize a preallocated WhereClause structure.
*/
static void whereClauseInit(WhereClause *pWC, Parse *pParse){
  pWC->pParse = pParse;
  pWC->nTerm = 0;

  struct ExprList_item *pTerm; /* A term of the ORDER BY clause */
  sqlite3 *db = pParse->db;

  assert( pOrderBy!=0 );
  nTerm = pOrderBy->nExpr;
  assert( nTerm>0 );









  /* Match terms of the ORDER BY clause against columns of
  ** the index.
  */
  for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<pIdx->nColumn; i++){
    Expr *pExpr;       /* The expression of the ORDER BY pTerm */
    CollSeq *pColl;    /* The collating sequence of pExpr */

  if( pTerm ){
    Expr *pExpr;
    *ppIndex = 0;
    bestFlags = WHERE_ROWID_EQ;
    if( pTerm->operator & WO_EQ ){
      /* Rowid== is always the best pick.  Look no further.  Because only
      ** a single row is generated, output is always in sorted order */
      *pFlags = WHERE_ROWID_EQ | WHERE_UNIQUE;
      *pnEq = 1;

      TRACE(("... best is rowid\n"));
      return 0.0;
    }else if( (pExpr = pTerm->pExpr)->pList!=0 ){
      /* Rowid IN (LIST): cost is NlogN where N is the number of list
      ** elements.  */
      lowestCost = pExpr->pList->nExpr;
      lowestCost *= estLog(lowestCost);

        }else if( pExpr->pList!=0 ){
          inMultiplier *= pExpr->pList->nExpr + 1.0;
        }
      }
    }
    cost = pProbe->aiRowEst[i] * inMultiplier * estLog(inMultiplier);
    nEq = i;
    if( pProbe->onError!=OE_None && (flags & WHERE_COLUMN_IN)==0
         && nEq==pProbe->nColumn ){
      flags |= WHERE_UNIQUE;
    }
    TRACE(("...... nEq=%d inMult=%.9g cost=%.9g\n", nEq, inMultiplier, cost));

    /* Look for range constraints
    */
    if( nEq<pProbe->nColumn ){
      int j = pProbe->aiColumn[nEq];
      pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);

  Bitmask notReady;          /* Cursors that are not yet positioned */
  WhereTerm *pTerm;          /* A single term in the WHERE clause */
  ExprMaskSet maskSet;       /* The expression mask set */
  WhereClause wc;            /* The WHERE clause is divided into these terms */
  struct SrcList_item *pTabItem;  /* A single entry from pTabList */
  WhereLevel *pLevel;             /* A single level in the pWInfo list */
  int iFrom;                      /* First unused FROM clause element */
  int andFlags;              /* AND-ed combination of all wc.a[].flags */

  /* The number of tables in the FROM clause is limited by the number of
  ** bits in a Bitmask 
  */
  if( pTabList->nSrc>BMS ){
    sqlite3ErrorMsg(pParse, "at most %d tables in a join", BMS);
    return 0;

  **
  ** This loop also figures out the nesting order of tables in the FROM
  ** clause.
  */
  notReady = ~(Bitmask)0;
  pTabItem = pTabList->a;
  pLevel = pWInfo->a;
  andFlags = ~0;
  for(i=iFrom=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){
    Index *pIdx;                /* Index for FROM table at pTabItem */
    int flags;                  /* Flags asssociated with pIdx */
    int nEq;                    /* Number of == or IN constraints */
    double cost;                /* The cost for pIdx */
    int j;                      /* For looping over FROM tables */
    Index *pBest = 0;           /* The best index seen so far */

      }
      if( (pTabItem->jointype & JT_LEFT)!=0
         || (j>0 && (pTabItem[-1].jointype & JT_LEFT)!=0)
      ){
        break;
      }
    }
    if( (bestFlags & WHERE_ORDERBY)!=0 ){
      *ppOrderBy = 0;
    }
    andFlags &= bestFlags;
    pLevel->flags = bestFlags;
    pLevel->pIdx = pBest;
    pLevel->nEq = bestNEq;
    pLevel->aInLoop = 0;
    pLevel->nIn = 0;
    if( pBest ){
      pLevel->iIdxCur = pParse->nTab++;
    }else{
      pLevel->iIdxCur = -1;
    }
    notReady &= ~getMask(&maskSet, pTabList->a[bestJ].iCursor);
    pLevel->iFrom = bestJ;
  }

  /* If the total query only selects a single row, then the ORDER BY
  ** clause is irrelevant.
  */
  if( (andFlags & WHERE_UNIQUE)!=0 && ppOrderBy ){
    *ppOrderBy = 0;
  }

  /* Open all tables in the pTabList and any indices selected for
  ** searching those tables.
  */
  sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */
  pLevel = pWInfo->a;
  for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){

#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the use of indices in WHERE clauses
# based on recent changes to the optimizer.
#
# $Id: where2.test,v 1.4 2005/07/29 19:43:59 drh Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Build some test data
#
do_test where2-1.0 {

  }
} {6 2 49 51 99 6 10000 10006 100 6 10201 10207 sort t1 {}}
do_test where2-6.4 {
  queryplan {
    SELECT * FROM t1 WHERE w=99 OR +w=100 OR 6=w ORDER BY +w
  }
} {6 2 49 51 99 6 10000 10006 100 6 10201 10207 sort t1 {}}

do_test where2-6.5 {
  queryplan {
    SELECT b.* FROM t1 a, t1 b
     WHERE a.w=1 AND (a.y=b.z OR b.z=10)
     ORDER BY +b.w
  }
} {1 0 4 4 2 1 9 10 sort a i1w b i1zyx}
do_test where2-6.6 {
  queryplan {
    SELECT b.* FROM t1 a, t1 b
     WHERE a.w=1 AND (b.z=10 OR a.y=b.z OR b.z=10)
     ORDER BY +b.w
  }
} {1 0 4 4 2 1 9 10 sort a i1w b i1zyx}




finish_test