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SQLite training in Houston TX on 2019-11-05 (details)
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Comment:Do not apply the WHERE-clause pushdown optimization to terms that originate in the ON or USING clause of a LEFT JOIN. Fix for ticket [c2a19d81652f40568c].
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SHA3-256: 52674f948c3e74e5cc32874d4885f2302ad1d5dd0bc45ff6bfda18cf4bea904a
User & Date: drh 2017-07-17 19:14:11
Context
2017-07-17
19:25
When checking for the WHERE-clause push-down optimization, verify that all terms of the compound inner SELECT are non-aggregate, not just the last term. Fix for ticket [f7f8c97e97597]. Closed-Leaf check-in: adc082c1 user: drh tags: push-down-backport
19:14
Do not apply the WHERE-clause pushdown optimization to terms that originate in the ON or USING clause of a LEFT JOIN. Fix for ticket [c2a19d81652f40568c]. check-in: 52674f94 user: drh tags: push-down-backport
19:07
For FROM-clause subqueries that cannot be flattened, try to push relevant WHERE clause terms of the outer query down into the subquery in order to help the subquery run faster and/or use less memory. Cherry-pick from [6df18e949d36]. Still need to backport bug fixes associated with that check-in. check-in: 043d6ce8 user: drh tags: push-down-backport
2015-08-22
01:32
Do not apply the WHERE-clause pushdown optimization to terms that originate in the ON or USING clause of a LEFT JOIN. Fix for ticket [c2a19d81652f40568c]. check-in: 351bc22f user: drh tags: trunk
Changes
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Changes to src/select.c.

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**
**   (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.)



**
** 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( 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;







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**
**   (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;

Changes to test/join5.test.

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  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;
} {}
























finish_test








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  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