SQLite

**
**   (3) The inner query has a LIMIT clause (since the changes to the WHERE
**       close would change the meaning of the LIMIT).
**
**   (4) The inner query is the right operand of a LEFT JOIN.  (The caller
**       enforces this restriction since this routine does not have enough
**       information to know.)
**
**   (5) The WHERE clause expression originates in the ON or USING clause
**       of a LEFT JOIN.
**
** Return 0 if no changes are made and non-zero if one or more WHERE clause
** terms are duplicated into the subquery.
*/
static int pushDownWhereTerms(
  sqlite3 *db,          /* The database connection (for malloc()) */
  Select *pSubq,        /* The subquery whose WHERE clause is to be augmented */

  if( pSubq->pLimit!=0 ){
     return 0; /* restriction (3) */
  }
  while( pWhere->op==TK_AND ){
    nChng += pushDownWhereTerms(db, pSubq, pWhere->pRight, iCursor);
    pWhere = pWhere->pLeft;
  }
  if( ExprHasProperty(pWhere,EP_FromJoin) ) return 0; /* restriction 5 */
  if( sqlite3ExprIsTableConstant(pWhere, iCursor) ){
    nChng++;
    while( pSubq ){
      pNew = sqlite3ExprDup(db, pWhere, 0);
      pNew = substExpr(db, pNew, iCursor, pSubq->pEList);
      pSubq->pWhere = sqlite3ExprAnd(db, pSubq->pWhere, pNew);
      pSubq = pSubq->pPrior;

  CREATE TABLE x2(b NOT NULL);
  CREATE TABLE x3(c, d);
  INSERT INTO x3 VALUES('a', NULL);
  INSERT INTO x3 VALUES('b', NULL);
  INSERT INTO x3 VALUES('c', NULL);
  SELECT * FROM x1 LEFT JOIN x2 JOIN x3 WHERE x3.d = x2.b;
} {}

# Ticket https://www.sqlite.org/src/tktview/c2a19d81652f40568c770c43 on
# 2015-08-20.  LEFT JOIN and the push-down optimization.
#
do_execsql_test join6-4.1 {
  SELECT *
  FROM (
      SELECT 'apple' fruit
      UNION ALL SELECT 'banana'
  ) a
  JOIN (
      SELECT 'apple' fruit
      UNION ALL SELECT 'banana'
  ) b ON a.fruit=b.fruit
  LEFT JOIN (
      SELECT 1 isyellow
  ) c ON b.fruit='banana';
} {apple apple {} banana banana 1}
do_execsql_test join6-4.2 {
  SELECT *
    FROM (SELECT 'apple' fruit UNION ALL SELECT 'banana')
         LEFT JOIN (SELECT 1) ON fruit='banana';
} {apple {} banana 1}

finish_test