SQLite

    static const u8 aEndOp[] = {
      OP_IdxGE,            /* 0: (end_constraints && !bRev && !endEq) */
      OP_IdxGT,            /* 1: (end_constraints && !bRev &&  endEq) */
      OP_IdxLE,            /* 2: (end_constraints &&  bRev && !endEq) */
      OP_IdxLT,            /* 3: (end_constraints &&  bRev &&  endEq) */
    };
    u16 nEq = pLoop->u.btree.nEq;     /* Number of == or IN terms */
    int isMinQuery = 0;          /* If this is an optimized SELECT min(x).. */
    int regBase;                 /* Base register holding constraint values */
    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 nConstraint;             /* Number of constraint terms */
    Index *pIdx;                 /* The index we will be using */
    int iIdxCur;                 /* The VDBE cursor for the index */
    int nExtraReg = 0;           /* Number of extra registers needed */
    int op;                      /* Instruction opcode */
    char *zStartAff;             /* Affinity for start of range constraint */
    char cEndAff = 0;            /* Affinity for end of range constraint */



    pIdx = pLoop->u.btree.pIndex;
    iIdxCur = pLevel->iIdxCur;
    assert( nEq>=pLoop->u.btree.nSkip );

    /* If this loop satisfies a sort order (pOrderBy) request that 
    ** was passed to this function to implement a "SELECT min(x) ..." 
    ** query, then the caller will only allow the loop to run for
    ** a single iteration. This means that the first row returned
    ** should not have a NULL value stored in 'x'. If column 'x' is
    ** the first one after the nEq equality constraints in the index,
    ** this requires some special handling.
    */
    if( (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN)!=0
     && (pWInfo->bOBSat!=0)
     && (pIdx->nKeyCol>nEq)
    ){
      assert( pLoop->u.btree.nSkip==0 );
      isMinQuery = 1;
      nExtraReg = 1;
    }

    /* Find any inequality constraint terms for the start and end 
    ** of the range. 
    */
    j = nEq;
    if( pLoop->wsFlags & WHERE_BTM_LIMIT ){
      pRangeStart = pLoop->aLTerm[j++];
      nExtraReg = 1;
    }
    if( pLoop->wsFlags & WHERE_TOP_LIMIT ){
      pRangeEnd = pLoop->aLTerm[j++];
      nExtraReg = 1;







    }

    /* 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,bRev,nExtraReg,&zStartAff);
    assert( zStartAff==0 || sqlite3Strlen30(zStartAff)>=nEq );
    if( zStartAff ) cEndAff = zStartAff[nEq];
    addrNxt = pLevel->addrNxt;

    /* 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( (nEq<pIdx->nKeyCol && bRev==(pIdx->aSortOrder[nEq]==SQLITE_SO_ASC))
     || (bRev && pIdx->nKeyCol==nEq)
    ){
      SWAP(WhereTerm *, pRangeEnd, pRangeStart);

    }

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

        }
        if( sqlite3ExprNeedsNoAffinityChange(pRight, zStartAff[nEq]) ){
          zStartAff[nEq] = SQLITE_AFF_NONE;
        }
      }  
      nConstraint++;
      testcase( pRangeStart->wtFlags & TERM_VIRTUAL );
    }else if( isMinQuery ){
      sqlite3VdbeAddOp2(v, OP_Null, 0, regBase+nEq);
      nConstraint++;
      startEq = 0;
      start_constraints = 1;
    }
    codeApplyAffinity(pParse, regBase, nConstraint, zStartAff);
    op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
    assert( op!=0 );
    testcase( op==OP_Rewind );
    testcase( op==OP_Last );
    testcase( op==OP_SeekGT );
    testcase( op==OP_SeekGE );
    testcase( op==OP_SeekLE );

      if( sqlite3CompareAffinity(pRight, cEndAff)!=SQLITE_AFF_NONE
       && !sqlite3ExprNeedsNoAffinityChange(pRight, cEndAff)
      ){
        codeApplyAffinity(pParse, regBase+nEq, 1, &cEndAff);
      }
      nConstraint++;
      testcase( pRangeEnd->wtFlags & TERM_VIRTUAL );




    }
    sqlite3DbFree(db, zStartAff);

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

    /* Check if the index cursor is past the end of the range. */
    if( pRangeEnd || nEq ){
      op = aEndOp[bRev*2 + endEq];
      testcase( op==OP_IdxGT );
      testcase( op==OP_IdxGE );
      testcase( op==OP_IdxLT );
      testcase( op==OP_IdxLE );
      sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
    }

    /* If there are inequality constraint upper bound but not a lower
    ** bound, then check that the value of the table column that the
    ** inequality contrains is not NULL since there is alway an implied
    ** lower bound of "column>NULL".
    */
    r1 = sqlite3GetTempReg(pParse);
    if( (pLoop->wsFlags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT))==WHERE_TOP_LIMIT 
     && (j = pIdx->aiColumn[nEq])>=0 
     && pIdx->pTable->aCol[j].notNull==0 
    ){
      sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, nEq, r1);
      VdbeComment((v, "%s", pIdx->pTable->aCol[j].zName));
      sqlite3VdbeAddOp2(v, OP_IsNull, r1, addrCont);
    }
    sqlite3ReleaseTempReg(pParse, r1);

    /* Seek the table cursor, if required */
    disableTerm(pLevel, pRangeStart);
    disableTerm(pLevel, pRangeEnd);
    if( omitTable ){
      /* pIdx is a covering index.  No need to access the main table. */
    }else if( HasRowid(pIdx->pTable) ){
      iRowidReg = iReleaseReg = sqlite3GetTempReg(pParse);

  count {SELECT w FROM t1 WHERE w==97 AND w==97}
} {97 2}
do_test where-1.34 {
  count {SELECT w FROM t1 WHERE w+1==98}
} {97 99}
do_test where-1.35 {
  count {SELECT w FROM t1 WHERE w<3}
} {1 2 2}
do_test where-1.36 {
  count {SELECT w FROM t1 WHERE w<=3}
} {1 2 3 3}
do_test where-1.37 {
  count {SELECT w FROM t1 WHERE w+1<=4 ORDER BY w}
} {1 2 3 99}

do_test where-1.38 {
  count {SELECT (w) FROM t1 WHERE (w)>(97)}
} {98 99 100 3}

  count {SELECT rowid FROM t1 WHERE w=1 AND +x IS NULL}
} {2 3}
do_test where4-1.5 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x>0}
} {1 2}
do_test where4-1.6 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x<9}
} {1 3}
do_test where4-1.7 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x IS NULL AND y=3}
} {2 2}
do_test where4-1.8 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x IS NULL AND y>2}
} {2 2}
do_test where4-1.9 {

  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL}
} {7 2}
do_test where4-1.14 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL AND y IS NULL}
} {7 2}
do_test where4-1.15 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL AND y<0}
} {2}
do_test where4-1.16 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL AND y>=0}
} {1}

do_test where4-2.1 {
  execsql {SELECT rowid FROM t1 ORDER BY w, x, y}
} {7 2 1 4 3 6 5}

do_test where8-1.8 {
  # 18 searches. 9 on the index cursor and 9 on the table cursor.
  execsql_status2 { SELECT c FROM t1 WHERE a > 1 AND c LIKE 'I%' }
} {II III IV IX 0 0 18}

do_test where8-1.9 {
  execsql_status2 { SELECT c FROM t1 WHERE a >= 9 OR b <= 'eight' }
} {IX X VIII 0 0 6}

do_test where8-1.10 {
  execsql_status2 { 
    SELECT c FROM t1 WHERE (a >= 9 AND c != 'X') OR b <= 'eight' 
  }
} {IX VIII 0 0 6}

do_test where8-1.11 {
  execsql_status2 { 
    SELECT c FROM t1 WHERE (a >= 4 AND a <= 6) OR b = 'nine' 
  }
} {IV V VI IX 0 0 10}