SQLite

  SelectDest dest;            /* How to deal with SELECT result */
  int nReg;                   /* Registers to allocate */
  Expr *pLimit;               /* New limit expression */

  Vdbe *v = pParse->pVdbe;
  assert( v!=0 );














  /* The evaluation of the EXISTS/SELECT must be repeated every time it
  ** is encountered if any of the following is true:
  **
  **    *  The right-hand side is a correlated subquery
  **    *  The right-hand side is an expression list containing variables
  **    *  We are inside a trigger
  **
  ** If all of the above are false, then we can run this code just once
  ** save the results, and reuse the same result on subsequent invocations.
  */
  if( !ExprHasProperty(pExpr, EP_VarSelect) ){
    /* If this routine has already been coded, then invoke it as a
    ** subroutine. */
    if( ExprHasProperty(pExpr, EP_Subrtn) ){
      sqlite3VdbeAddOp2(v, OP_Gosub, pExpr->y.sub.regReturn,
                        pExpr->y.sub.iAddr);
      return pExpr->iTable;
    }

    /* Begin coding the subroutine */
    ExprSetProperty(pExpr, EP_Subrtn);
    pExpr->y.sub.regReturn = ++pParse->nMem;
    pExpr->y.sub.iAddr =
      sqlite3VdbeAddOp2(v, OP_Integer, 0, pExpr->y.sub.regReturn) + 1;
    VdbeComment((v, "return address"));

    addrOnce = sqlite3VdbeAddOp0(v, OP_Once); VdbeCoverage(v);
  }
  
  /* For a SELECT, generate code to put the values for all columns of
  ** the first row into an array of registers and return the index of
  ** the first register.
  **

  if( sqlite3Select(pParse, pSel, &dest) ){
    return 0;
  }
  pExpr->iTable = rReg = dest.iSDParm;
  ExprSetVVAProperty(pExpr, EP_NoReduce);
  if( addrOnce ){
    sqlite3VdbeJumpHere(v, addrOnce);


    /* Subroutine return */
    sqlite3VdbeAddOp1(v, OP_Return, pExpr->y.sub.regReturn);
    sqlite3VdbeChangeP1(v, pExpr->y.sub.iAddr-1, sqlite3VdbeCurrentAddr(v)-1);
  }

  return rReg;
}
#endif /* SQLITE_OMIT_SUBQUERY */

#ifndef SQLITE_OMIT_SUBQUERY
/*
** Expr pIn is an IN(...) expression. This function checks that the 

}
do_eqp_test autoindex1-500.1 {
  SELECT b FROM t501
   WHERE t501.a IN (SELECT x FROM t502 WHERE y=?);
} {
  QUERY PLAN
  |--SEARCH TABLE t501 USING INTEGER PRIMARY KEY (rowid=?)
  `--LIST SUBQUERY xxxxxx
     `--SCAN TABLE t502
}
do_eqp_test autoindex1-501 {
  SELECT b FROM t501
   WHERE t501.a IN (SELECT x FROM t502 WHERE y=t501.b);
} {
  QUERY PLAN
  |--SCAN TABLE t501
  `--CORRELATED LIST SUBQUERY xxxxxx
     `--SEARCH TABLE t502 USING AUTOMATIC COVERING INDEX (y=?)
}
do_eqp_test autoindex1-502 {
  SELECT b FROM t501
   WHERE t501.a=123
     AND t501.a IN (SELECT x FROM t502 WHERE y=t501.b);
} {
  QUERY PLAN
  |--SEARCH TABLE t501 USING INTEGER PRIMARY KEY (rowid=?)
  `--CORRELATED LIST SUBQUERY xxxxxx
     `--SCAN TABLE t502
}

# The following code checks a performance regression reported on the
# mailing list on 2010-10-19.  The problem is that the nRowEst field
# of ephermeral tables was not being initialized correctly and so no
# automatic index was being created for the emphemeral table when it was

}

det 3.3.1 {
  SELECT * FROM t1 WHERE y IN (SELECT y FROM t2)
} {
  QUERY PLAN
  |--SCAN TABLE t1
  `--LIST SUBQUERY xxxxxx
     `--SCAN TABLE t2
}
det 3.3.2 {
  SELECT * FROM t1 WHERE y IN (SELECT y FROM t2 WHERE t1.x!=t2.x)
} {
  QUERY PLAN
  |--SCAN TABLE t1
  `--CORRELATED LIST SUBQUERY xxxxxx
     `--SCAN TABLE t2
}
det 3.3.3 {
  SELECT * FROM t1 WHERE EXISTS (SELECT y FROM t2 WHERE t1.x!=t2.x)
} {
  QUERY PLAN
  |--SCAN TABLE t1

do_eqp_test 5.1 {
  SELECT * FROM d2 WHERE 
    (a, b) IN (SELECT x, y FROM d1) AND
    (c) IN (SELECT y FROM d1)
} {
  QUERY PLAN
  |--SEARCH TABLE d2 USING INDEX d2ab (a=? AND b=?)
  |--LIST SUBQUERY xxxxxx
  |  `--SCAN TABLE d1
  `--LIST SUBQUERY xxxxxx
     `--SCAN TABLE d1
}

do_execsql_test 6.0 {
  CREATE TABLE e1(a, b, c, d, e);
  CREATE INDEX e1ab ON e1(a, b);
  CREATE INDEX e1cde ON e1(c, d, e);