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Comment:Fix the count-of-view optimization so that it is (correctly) disabled for a query that includes a WHERE clause or a GROUP BY clause.
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SHA3-256: 05897ca48a40c6771ff83ba8ecc3a5c60dafddf58651c222dd8cf89b9fc7b077
User & Date: drh 2019-05-15 18:42:15
References
2019-06-03
13:53
Fix the count-of-view optimization so that it is (correctly) disabled for a query that includes a WHERE clause or a GROUP BY clause. Cherrypick of [05897ca48a40c6771]. check-in: 583e5a0ab6 user: mistachkin tags: branch-3.28
Context
2019-06-03
13:53
Fix the count-of-view optimization so that it is (correctly) disabled for a query that includes a WHERE clause or a GROUP BY clause. Cherrypick of [05897ca48a40c6771]. check-in: 583e5a0ab6 user: mistachkin tags: branch-3.28
2019-05-16
01:22
Make sure the OP_Concat opcode always correctly zero-terminates a UTF16 string, even if the input strings are ill-formed. This is a followup to check-in [3a16ddf91f0c9c516a7] that fixes a case the previous check-in missed. Also add assert()s to prove correct zero termination. check-in: d612fb7873 user: drh tags: trunk
2019-05-15
18:42
Fix the count-of-view optimization so that it is (correctly) disabled for a query that includes a WHERE clause or a GROUP BY clause. check-in: 05897ca48a user: drh tags: trunk
10:16
Simplify the "Verifying Code Authenticity" section of the README.md file. No code changes. check-in: adebffc18e user: drh tags: trunk
Changes
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Changes to src/select.c.

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**    SELECT (SELECT count(*) FROM t1)+(SELECT count(*) FROM t2)
**
** The transformation only works if all of the following are true:
**
**   *  The subquery is a UNION ALL of two or more terms
**   *  The subquery does not have a LIMIT clause
**   *  There is no WHERE or GROUP BY or HAVING clauses on the subqueries
**   *  The outer query is a simple count(*)

**
** Return TRUE if the optimization is undertaken.
*/
static int countOfViewOptimization(Parse *pParse, Select *p){
  Select *pSub, *pPrior;
  Expr *pExpr;
  Expr *pCount;
  sqlite3 *db;
  if( (p->selFlags & SF_Aggregate)==0 ) return 0;   /* This is an aggregate */
  if( p->pEList->nExpr!=1 ) return 0;               /* Single result column */


  pExpr = p->pEList->a[0].pExpr;
  if( pExpr->op!=TK_AGG_FUNCTION ) return 0;        /* Result is an aggregate */
  if( sqlite3_stricmp(pExpr->u.zToken,"count") ) return 0;  /* Is count() */
  if( pExpr->x.pList!=0 ) return 0;                 /* Must be count(*) */
  if( p->pSrc->nSrc!=1 ) return 0;                  /* One table in FROM  */
  pSub = p->pSrc->a[0].pSelect;
  if( pSub==0 ) return 0;                           /* The FROM is a subquery */







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**    SELECT (SELECT count(*) FROM t1)+(SELECT count(*) FROM t2)
**
** The transformation only works if all of the following are true:
**
**   *  The subquery is a UNION ALL of two or more terms
**   *  The subquery does not have a LIMIT clause
**   *  There is no WHERE or GROUP BY or HAVING clauses on the subqueries
**   *  The outer query is a simple count(*) with no WHERE clause or other
**      extraneous syntax.
**
** Return TRUE if the optimization is undertaken.
*/
static int countOfViewOptimization(Parse *pParse, Select *p){
  Select *pSub, *pPrior;
  Expr *pExpr;
  Expr *pCount;
  sqlite3 *db;
  if( (p->selFlags & SF_Aggregate)==0 ) return 0;   /* This is an aggregate */
  if( p->pEList->nExpr!=1 ) return 0;               /* Single result column */
  if( p->pWhere ) return 0;
  if( p->pGroupBy ) return 0;
  pExpr = p->pEList->a[0].pExpr;
  if( pExpr->op!=TK_AGG_FUNCTION ) return 0;        /* Result is an aggregate */
  if( sqlite3_stricmp(pExpr->u.zToken,"count") ) return 0;  /* Is count() */
  if( pExpr->x.pList!=0 ) return 0;                 /* Must be count(*) */
  if( p->pSrc->nSrc!=1 ) return 0;                  /* One table in FROM  */
  pSub = p->pSrc->a[0].pSelect;
  if( pSub==0 ) return 0;                           /* The FROM is a subquery */

Changes to test/countofview.test.

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} {1}

do_execsql_test 1.3 {
  select count(*) from (
    select c from t2 union all select f from t3
  )
} {3}














finish_test








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} {1}

do_execsql_test 1.3 {
  select count(*) from (
    select c from t2 union all select f from t3
  )
} {3}

# 2019-05-15
do_execsql_test 2.0 {
  CREATE TABLE t1(x);
  INSERT INTO t1 VALUES(1),(99),('abc');
  CREATE VIEW v1(x,y) AS SELECT x,1 FROM t1 UNION ALL SELECT x,2 FROM t1;
  SELECT count(*) FROM v1 WHERE x<>1;
} {4}
do_execsql_test 2.1 {
  SELECT count(*) FROM v1 GROUP BY y;
} {3 3}



finish_test