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 1.127 2005/01/03 18:13:18 tpoindex 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.

      assert( pTerm->idxLeft==iCur );
      assert( omitTable==0 );
      brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
      codeEqualityTerm(pParse, pTerm, brk, pLevel);
      cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
      sqlite3VdbeAddOp(v, OP_MustBeInt, 1, brk);
      sqlite3VdbeAddOp(v, OP_NotExists, iCur, brk);
      VdbeComment((v, "pk"));
      pLevel->op = OP_Noop;
    }else if( pIdx!=0 && pLevel->score>3 && (pLevel->score&0x0c)==0 ){
      /* Case 2:  There is an index and all terms of the WHERE clause that
      **          refer to the index using the "==" or "IN" operators.
      */
      int start;
      int nColumn = (pLevel->score+16)/32;

        pTerm = &aExpr[k];
        pX = pTerm->p;
        assert( pX!=0 );
        assert( pTerm->idxLeft==iCur );
        sqlite3ExprCode(pParse, pX->pRight);
        sqlite3VdbeAddOp(v, OP_ForceInt, pX->op==TK_LT || pX->op==TK_GT, brk);
        sqlite3VdbeAddOp(v, bRev ? OP_MoveLt : OP_MoveGe, iCur, brk);
        VdbeComment((v, "pk"));
        disableTerm(pLevel, &pTerm->p);
      }else{
        sqlite3VdbeAddOp(v, bRev ? OP_Last : OP_Rewind, iCur, brk);
      }
      if( iDirectLt[i]>=0 ){
        Expr *pX;
        k = iDirectLt[i];