SQLite

    return pVector;
  }else if( pVector->flags & EP_xIsSelect ){
    return pVector->x.pSelect->pEList->a[i].pExpr;
  }
  return pVector->x.pList->a[i].pExpr;
}

/*
** If expression pExpr is of type TK_SELECT, generate code to evaluate
** it. Return the register in which the result is stored (or, if the 
** sub-select returns more than one column, the first in an array
** of registers in which the result is stored).
**
** If pExpr is not a TK_SELECT expression, return 0.
*/
static int exprCodeSubselect(Parse *pParse, Expr *pExpr){
  int reg = 0;


  if( pExpr->op==TK_SELECT ){


    reg = sqlite3CodeSubselect(pParse, pExpr, 0, 0);
  }
  return reg;
}

/*
** Argument pVector points to a vector expression - either a TK_VECTOR
** or TK_SELECT that returns more than one column. This function generates
** code to evaluate expression iElem of the vector. The number of the
** register containing the result is returned. 
**
** Before returning, output parameter (*ppExpr) is set to point to the
** Expr object corresponding to element iElem of the vector.
**
** If pVector is a TK_SELECT expression, then argument regSelect is 
** passed the first in an array of registers that contain the results
** of the sub-select. 
**
** If output parameter (*pRegFree) is set to a non-zero value by this
** function, it is the value of a temporary register that should be
** freed by the caller.
*/
static int exprVectorRegister(
  Parse *pParse,                  /* Parse context */
  Expr *pVector,                  /* Vector to extract element from */
  int iElem,                      /* Element to extract from pVector */
  int regSelect,                  /* First in array of registers */
  Expr **ppExpr,                  /* OUT: Expression element */
  int *pRegFree                   /* OUT: Temp register to free */
){
  if( regSelect ){
    *ppExpr = pVector->x.pSelect->pEList->a[iElem].pExpr;
     return regSelect+iElem;
  }
  *ppExpr = pVector->x.pList->a[iElem].pExpr;
  return sqlite3ExprCodeTemp(pParse, *ppExpr, pRegFree);
}

/*
** Expression pExpr is a comparison between two vector values. Compute
** the result of the comparison and write it to register dest.
*/
static void codeVectorCompare(Parse *pParse, Expr *pExpr, int dest){
  Vdbe *v = pParse->pVdbe;
  Expr *pLeft = pExpr->pLeft;
  Expr *pRight = pExpr->pRight;
  int nLeft = sqlite3ExprVectorSize(pLeft);
  int nRight = sqlite3ExprVectorSize(pRight);
  int addr = sqlite3VdbeMakeLabel(v);

  /* Check that both sides of the comparison are vectors, and that
  ** both are the same length.  */
  if( nLeft!=nRight ){
    sqlite3ErrorMsg(pParse, "invalid use of row value");
  }else{
    int p5 = (pExpr->op==TK_IS || pExpr->op==TK_ISNOT) ? SQLITE_NULLEQ : 0;
    int opCmp;

    int i;
    int p3 = 0;
    int p4 = 0;
    int regLeft = 0;
    int regRight = 0;
    int regTmp = 0;

    assert( pExpr->op==TK_EQ || pExpr->op==TK_NE 
         || pExpr->op==TK_IS || pExpr->op==TK_ISNOT 
         || pExpr->op==TK_LT || pExpr->op==TK_GT 
         || pExpr->op==TK_LE || pExpr->op==TK_GE 
    );

    if( pExpr->op==TK_EQ || pExpr->op==TK_NE ){





      regTmp = sqlite3GetTempReg(pParse);





      sqlite3VdbeAddOp2(v, OP_Integer, (pExpr->op==TK_EQ), dest);








    }

    regLeft = exprCodeSubselect(pParse, pLeft);
    regRight = exprCodeSubselect(pParse, pRight);


    for(i=0; i<nLeft; i++){
      int regFree1 = 0, regFree2 = 0;
      Expr *pL, *pR; 
      int r1, r2;

      if( i ) sqlite3ExprCachePush(pParse);
      r1 = exprVectorRegister(pParse, pLeft, i, regLeft, &pL, &regFree1);
      r2 = exprVectorRegister(pParse, pRight, i, regRight, &pR, &regFree2);

      switch( pExpr->op ){
        case TK_IS:
          codeCompare(
              pParse, pL, pR, OP_Eq, r1, r2, dest, SQLITE_STOREP2|SQLITE_NULLEQ
          );
          sqlite3VdbeAddOp3(v, OP_IfNot, dest, addr, 1);
          VdbeCoverage(v);
          break;

        case TK_ISNOT:
          codeCompare(
              pParse, pL, pR, OP_Ne, r1, r2, dest, SQLITE_STOREP2|SQLITE_NULLEQ
          );
          sqlite3VdbeAddOp3(v, OP_If, dest, addr, 1);
          VdbeCoverage(v);
          break;

        case TK_EQ:
        case TK_NE:
          codeCompare(pParse, pL, pR, OP_Cmp, r1, r2, regTmp,SQLITE_STOREP2|p5);
          sqlite3VdbeAddOp4Int(
              v, OP_CmpTest, regTmp, addr, dest, pExpr->op==TK_NE
          );
          VdbeCoverage(v);
          break;


        case TK_LT:

        case TK_LE:
        case TK_GT:
        case TK_GE:
          codeCompare(pParse, pL, pR, OP_Cmp, r1, r2, dest, SQLITE_STOREP2|p5);
          sqlite3VdbeAddOp4Int(v, OP_CmpTest, dest, addr, 0, pExpr->op);
          VdbeCoverage(v);
          break;
      }



      sqlite3ReleaseTempReg(pParse, regFree1);
      sqlite3ReleaseTempReg(pParse, regFree2);
      if( i ) sqlite3ExprCachePop(pParse);
    }

    sqlite3ReleaseTempReg(pParse, regTmp);
  }

  sqlite3VdbeResolveLabel(v, addr);
}

#if SQLITE_MAX_EXPR_DEPTH>0
/*

*/
/* Opcode: Ge P1 P2 P3 P4 P5
** Synopsis: if r[P1]>=r[P3] goto P2
**
** This works just like the Lt opcode except that the jump is taken if
** the content of register P3 is greater than or equal to the content of
** register P1.  See the Lt opcode for additional information.
**
** Opcode: Cmp P1 P2 P3 P4 P5
** Synopsis: P2 = cmp(P1, P3)
**
** The SQLITE_STOREP2 flag must be set for this opcode. It compares the
** values in registers P1 and P3 and stores the result of the comparison
** in register P2. The results is NULL if either of the two operands are
** NULL. Otherwise, it is an integer value less than zero, zero or greater 
** than zero if P3 is less than, equal to or greater than P1, respectively.
*/
case OP_Cmp:              /* in1, in3 */
case OP_Eq:               /* same as TK_EQ, jump, in1, in3 */
case OP_Ne:               /* same as TK_NE, jump, in1, in3 */
case OP_Lt:               /* same as TK_LT, jump, in1, in3 */
case OP_Le:               /* same as TK_LE, jump, in1, in3 */
case OP_Gt:               /* same as TK_GT, jump, in1, in3 */
case OP_Ge: {             /* same as TK_GE, jump, in1, in3 */
  int res;            /* Result of the comparison of pIn1 against pIn3 */
  char affinity;      /* Affinity to use for comparison */
  u16 flags1;         /* Copy of initial value of pIn1->flags */
  u16 flags3;         /* Copy of initial value of pIn3->flags */

  assert( pOp->opcode!=OP_Cmp || (pOp->p5 & SQLITE_STOREP2) );
  pIn1 = &aMem[pOp->p1];
  pIn3 = &aMem[pOp->p3];
  flags1 = pIn1->flags;
  flags3 = pIn3->flags;
  if( (flags1 | flags3)&MEM_Null ){
    /* One or both operands are NULL */
    if( pOp->p5 & SQLITE_NULLEQ ){

  }else if( eqOnly ){
    assert( pOp[1].opcode==OP_IdxLT || pOp[1].opcode==OP_IdxGT );
    pOp++; /* Skip the OP_IdxLt or OP_IdxGT that follows */
  }
  break;
}

/* Opcode: CmpTest P1 P2 P3 P4 *
**
** P2 is a jump destination. Register P1 is guaranteed to contain either
** an integer value or a NULL. 
**
** If P3 is non-zero, it identifies an output register. In this case, if
** P1 is NULL, P3 is also set to NULL. Or, if P1 is any integer value 
** other than 0, P3 is set to the value of P4 and a jump to P2 is taken.
**
** If P3 is 0, the jump is taken if P1 contains any value other than 0 (i.e.
** NULL does cause a jump). Additionally, if P1 is not NULL, its value is
** modified to integer value 0 or 1 according to the value of the P4 integer
** operand:
**
**   P4            modification
**   --------------------------
**   OP_Lt         (P1 = (P1 < 0))
**   OP_Le         (P1 = (P1 <= 0))
**   OP_Gt         (P1 = (P1 > 0))
**   OP_Ge         (P1 = (P1 >= 0))
*/
case OP_CmpTest: {                /* in1, jump */
  int bJump;
  pIn1 = &aMem[pOp->p1];

  if( pOp->p3 ){
    bJump = 0;
    if( pIn1->flags & MEM_Null ){
      memAboutToChange(p, &aMem[pOp->p3]);
      MemSetTypeFlag(&aMem[pOp->p3], MEM_Null);
    }else if( pIn1->u.i!=0 ){
      memAboutToChange(p, &aMem[pOp->p3]);
      MemSetTypeFlag(&aMem[pOp->p3], MEM_Int);
      aMem[pOp->p3].u.i = pOp->p4.i;
      bJump = 1;
    }
  }else{
    if( (pIn1->flags & MEM_Int) ){
      bJump = (pIn1->u.i!=0);
      switch( pOp->p4.i ){
        case OP_Lt: pIn1->u.i = (pIn1->u.i < 0); break;
        case OP_Le: pIn1->u.i = (pIn1->u.i <= 0); break;
        case OP_Gt: pIn1->u.i = (pIn1->u.i > 0); break;
        default: 
          assert( pOp->p4.i==OP_Ge ); 
          pIn1->u.i = (pIn1->u.i >= 0); 
          break;
      }
    }else{
      bJump = 1;
    }
  }

  if( bJump ) goto jump_to_p2;
  break;
}

/* Opcode: Found P1 P2 P3 P4 *

foreach {tn v1 v2 eq ne is isnot} {
  1 "1, 2, 3"    "1, 2, 3"                   1  0     1 0
  2 "1, 0, 3"    "1, 2, 3"                   0  1     0 1
  3 "1, 2, NULL" "1, 2, 3"                   {} {}    0 1
  4 "1, 2, NULL" "1, 2, NULL"                {} {}    1 0
  5 "NULL, NULL, NULL" "NULL, NULL, NULL"    {} {}    1 0

  6 "1, NULL, 1" "1, 1, 1"                   {} {}    0 1
  7 "1, NULL, 1" "1, 1, 2"                   0  1     0 1
} {
  do_execsql_test 1.$tn.eq "SELECT ($v1) == ($v2)" [list $eq]
  do_execsql_test 1.$tn.ne "SELECT ($v1) != ($v2)" [list $ne]

  do_execsql_test 1.$tn.is    "SELECT ($v1) IS ($v2)"     [list $is]
  do_execsql_test 1.$tn.isnot "SELECT ($v1) IS NOT ($v2)" [list $isnot]