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 1.302 2008/04/19 14:40:44 drh Exp $
*/
#include "sqliteInt.h"

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

    int nTerm;
    WHERETRACE(("Recomputing index info for %s...\n", pTab->zName));

    /* Count the number of possible WHERE clause constraints referring
    ** to this virtual table */
    for(i=nTerm=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
      if( pTerm->leftCursor != pSrc->iCursor ) continue;
      if( (pTerm->eOperator&(pTerm->eOperator-1))==0 );
      testcase( pTerm->eOperator==WO_IN );
      testcase( pTerm->eOperator==WO_ISNULL );
      if( pTerm->eOperator & (WO_IN|WO_ISNULL) ) continue;
      nTerm++;
    }

    /* If the ORDER BY clause contains only columns in the current 
    ** virtual table then allocate space for the aOrderBy part of
    ** the sqlite3_index_info structure.
    */

    *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint = pIdxCons;
    *(struct sqlite3_index_orderby**)&pIdxInfo->aOrderBy = pIdxOrderBy;
    *(struct sqlite3_index_constraint_usage**)&pIdxInfo->aConstraintUsage =
                                                                     pUsage;

    for(i=j=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){
      if( pTerm->leftCursor != pSrc->iCursor ) continue;
      if( (pTerm->eOperator&(pTerm->eOperator-1))==0 );
      testcase( pTerm->eOperator==WO_IN );
      testcase( pTerm->eOperator==WO_ISNULL );
      if( pTerm->eOperator & (WO_IN|WO_ISNULL) ) continue;
      pIdxCons[j].iColumn = pTerm->leftColumn;
      pIdxCons[j].iTermOffset = i;
      pIdxCons[j].op = pTerm->eOperator;
      /* The direct assignment in the previous line is possible only because
      ** the WO_ and SQLITE_INDEX_CONSTRAINT_ codes are identical.  The
      ** following asserts verify this fact. */
      assert( WO_EQ==SQLITE_INDEX_CONSTRAINT_EQ );

    pTerm = findTerm(pWC, iCur, k, notReady, pLevel->flags, pIdx);
    if( pTerm==0 ) break;
    assert( (pTerm->flags & TERM_CODED)==0 );
    r1 = codeEqualityTerm(pParse, pTerm, pLevel, regBase+j);
    if( r1!=regBase+j ){
      sqlite3VdbeAddOp2(v, OP_SCopy, r1, regBase+j);
    }
    testcase( pTerm->eOperator & WO_ISNULL );
    testcase( pTerm->eOperator & WO_IN );
    if( (pTerm->eOperator & (WO_ISNULL|WO_IN))==0 ){
      sqlite3VdbeAddOp2(v, OP_IsNull, regBase+j, pLevel->brk);
    }
  }
  return regBase;
}

        sqlite3VdbeAddOp3(v, testOp, pLevel->iMem, brk, r1);
        sqlite3VdbeChangeP5(v, SQLITE_AFF_NUMERIC | SQLITE_JUMPIFNULL);
        sqlite3ReleaseTempReg(pParse, r1);
      }
    }else if( pLevel->flags & (WHERE_COLUMN_RANGE|WHERE_COLUMN_EQ) ){
      /* Case 3: A scan using an index.
      **
      **         The WHERE clause may contain zero or more equality 
      **         terms ("==" or "IN" operators) that refer to the N
      **         left-most columns of the index. It may also contain
      **         inequality constraints (>, <, >= or <=) on the indexed
      **         column that immediately follows the N equalities. Only 
      **         the right-most column can be an inequality - the rest must
      **         use the "==" and "IN" operators. For example, if the 
      **         index is on (x,y,z), then the following clauses are all 
      **         optimized:
      **
      **            x=5
      **            x=5 AND y=10
      **            x=5 AND y<10
      **            x=5 AND y>5 AND y<10
      **            x=5 AND y=5 AND z<=10
      **
      **         The z<10 term of the following cannot be used, only
      **         the x=5 term:
      **
      **            x=5 AND z<10
      **
      **         N may be zero if there are inequality constraints.
      **         If there are no inequality constraints, then N is at
      **         least one.
      **
      **         This case is also used when there are no WHERE clause
      **         constraints but an index is selected anyway, in order
      **         to force the output order to conform to an ORDER BY.
      */  
      int aStartOp[] = {
        0,

      int r1;                      /* Temp register */
      WhereTerm *pRangeStart = 0;  /* Inequality constraint at range start */
      WhereTerm *pRangeEnd = 0;    /* Inequality constraint at range end */
      int startEq;                 /* True if range start uses ==, >= or <= */
      int endEq;                   /* True if range end uses ==, >= or <= */
      int start_constraints;       /* Start of range is constrained */
      int k = pIdx->aiColumn[nEq]; /* Column for inequality constraints */
      int nConstraint;             /* Number of constraint terms */
      int op;

      /* Generate code to evaluate all constraint terms using == or IN
      ** and store the values of those terms in an array of registers
      ** starting at regBase.
      */
      regBase = codeAllEqualityTerms(pParse, pLevel, &wc, notReady, 2);

        pRangeStart = findTerm(&wc, iCur, k, notReady, (WO_GT|WO_GE), pIdx);
      }

      /* If we are doing a reverse order scan on an ascending index, or
      ** a forward order scan on a descending index, interchange the 
      ** start and end terms (pRangeStart and pRangeEnd).
      */
      if( bRev==(pIdx->aSortOrder[nEq]==SQLITE_SO_ASC) ){
        SWAP(WhereTerm *, pRangeEnd, pRangeStart);
      }

      testcase( pRangeStart && pRangeStart->eOperator & WO_LE );
      testcase( pRangeStart && pRangeStart->eOperator & WO_GE );
      testcase( pRangeEnd && pRangeEnd->eOperator & WO_LE );
      testcase( pRangeEnd && pRangeEnd->eOperator & WO_GE );
      startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);
      endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);
      start_constraints = pRangeStart || nEq>0;

      /* Seek the index cursor to the start of the range. */
      nConstraint = nEq;
      if( pRangeStart ){
        int dcc = pParse->disableColCache;
        if( pRangeEnd ){
          pParse->disableColCache = 1;
        }
        sqlite3ExprCode(pParse, pRangeStart->pExpr->pRight, regBase+nEq);
        pParse->disableColCache = dcc;
        sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, nxt);
        nConstraint++;
      }else if( isMinQuery ){
        sqlite3VdbeAddOp2(v, OP_Null, 0, regBase+nEq);
        nConstraint++;
        startEq = 0;
        start_constraints = 1;
      }
      codeApplyAffinity(pParse, regBase, nConstraint, pIdx);
      op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
      assert( op!=0 );
      testcase( op==OP_Rewind );
      testcase( op==OP_Last );
      testcase( op==OP_MoveGt );
      testcase( op==OP_MoveGe );
      testcase( op==OP_MoveLe );
      testcase( op==OP_MoveLt );
      sqlite3VdbeAddOp4(v, op, iIdxCur, nxt, regBase, 
                        (char*)nConstraint, P4_INT32);

      /* Load the value for the inequality constraint at the end of the
      ** range (if any).
      */
      nConstraint = nEq;
      if( pRangeEnd ){
        sqlite3ExprCode(pParse, pRangeEnd->pExpr->pRight, regBase+nEq);
        sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, nxt);
        codeApplyAffinity(pParse, regBase, nEq+1, pIdx);
        nConstraint++;
      }

      /* Top of the loop body */
      pLevel->p2 = sqlite3VdbeCurrentAddr(v);

      /* Check if the index cursor is past the end of the range. */
      op = aEndOp[(pRangeEnd || nEq) * (1 + bRev)];
      testcase( op==OP_Noop );
      testcase( op==OP_IdxGE );
      testcase( op==OP_IdxLT );
      sqlite3VdbeAddOp4(v, op, iIdxCur, nxt, regBase,
                        (char*)nConstraint, P4_INT32);
      sqlite3VdbeChangeP5(v, endEq!=bRev);

      /* If there are inequality constraints, check that the value

      ** of the table column that the inequality contrains is not NULL.
      ** If it is, jump to the next iteration of the loop.
      */
      r1 = sqlite3GetTempReg(pParse);
      testcase( pLevel->flags & WHERE_BTM_LIMIT );
      testcase( pLevel->flags & WHERE_TOP_LIMIT );
      if( pLevel->flags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT) ){
        sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, nEq, r1);
        sqlite3VdbeAddOp2(v, OP_IsNull, r1, cont);
      }

      /* Seek the table cursor, if required */
      if( !omitTable ){
        sqlite3VdbeAddOp2(v, OP_IdxRowid, iIdxCur, r1);
        sqlite3VdbeAddOp3(v, OP_MoveGe, iCur, 0, r1);  /* Deferred seek */
      }
      sqlite3ReleaseTempReg(pParse, r1);

      /* Record the instruction used to terminate the loop. Disable 
      ** WHERE clause terms made redundant by the index range scan.
      */
      pLevel->op = bRev ? OP_Prev : OP_Next;
      pLevel->p1 = iIdxCur;
      disableTerm(pLevel, pRangeStart);
      disableTerm(pLevel, pRangeEnd);
    }else{
      /* Case 4:  There is no usable index.  We must do a complete
      **          scan of the entire table.
      */
      assert( omitTable==0 );
      assert( bRev==0 );
      pLevel->op = OP_Next;
      pLevel->p1 = iCur;
      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, OP_Rewind, iCur, brk);
    }
    notReady &= ~getMask(&maskSet, iCur);

    /* Insert code to test every subexpression that can be completely
    ** computed using the current set of tables.
    */
    for(pTerm=wc.a, j=wc.nTerm; j>0; j--, pTerm++){
      Expr *pE;
      testcase( pTerm->flags & TERM_VIRTUAL );
      testcase( pTerm->flags & TERM_CODED );
      if( pTerm->flags & (TERM_VIRTUAL|TERM_CODED) ) continue;
      if( (pTerm->prereqAll & notReady)!=0 ) continue;
      pE = pTerm->pExpr;
      assert( pE!=0 );
      if( pLevel->iLeftJoin && !ExprHasProperty(pE, EP_FromJoin) ){
        continue;
      }

    if( pLevel->iLeftJoin ){
      pLevel->top = sqlite3VdbeCurrentAddr(v);
      sqlite3VdbeAddOp2(v, OP_Integer, 1, pLevel->iLeftJoin);
      VdbeComment((v, "record LEFT JOIN hit"));
      sqlite3ExprClearColumnCache(pParse, pLevel->iTabCur);
      sqlite3ExprClearColumnCache(pParse, pLevel->iIdxCur);
      for(pTerm=wc.a, j=0; j<wc.nTerm; j++, pTerm++){
        testcase( pTerm->flags & TERM_VIRTUAL );
        testcase( pTerm->flags & TERM_CODED );
        if( pTerm->flags & (TERM_VIRTUAL|TERM_CODED) ) continue;
        if( (pTerm->prereqAll & notReady)!=0 ) continue;
        assert( pTerm->pExpr );
        sqlite3ExprIfFalse(pParse, pTerm->pExpr, cont, SQLITE_JUMPIFNULL);
        pTerm->flags |= TERM_CODED;
      }
    }

        nQPlan += 2;
      }else{
        memcpy(&sqlite3_query_plan[nQPlan], z, n);
        nQPlan += n;
      }
      sqlite3_query_plan[nQPlan++] = ' ';
    }
    testcase( pLevel->flags & WHERE_ROWID_EQ );
    testcase( pLevel->flags & WHERE_ROWID_RANGE );
    if( pLevel->flags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){
      memcpy(&sqlite3_query_plan[nQPlan], "* ", 2);
      nQPlan += 2;
    }else if( pLevel->pIdx==0 ){
      memcpy(&sqlite3_query_plan[nQPlan], "{} ", 3);
      nQPlan += 3;
    }else{