SQLite

Check-in [21235d9a41]
Login

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Fix the handling of sub-queries with LIMIT clauses by the optimization activated by compile-time symbol SQLITE_COUNTOFVIEW_OPTIMIZATION.
Downloads: Tarball | ZIP archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA3-256: 21235d9a41567897418aa12f7bd6dd8d6ee363147527e1d8fbca14fc83e0f2c9
User & Date: dan 2018-08-03 20:19:52.614
Context
2018-08-04
15:16
Ensure that all expressions that are to be evaluated once at the start of a prepared statement (the Parse.pConstExpr expressions) pass the sqlite3ExprIsConstantNotJoin() test. It is not sufficient to pass just the sqlite3ExprIsConstant() test as that would allow through column references that are bound to constants by the WHERE clause in the constant propagation optimization. This fixes a problem discovered by OSSFuzz. (check-in: 8bc7f84c39 user: drh tags: trunk)
2018-08-03
23:04
Completely remove the column cache logic, which has been a persistent source of bugs for many years. Due to recent enhancements to the performance of the OP_Column opcode, removing the column cache actually makes speed-check.sh run faster. Removing the column cache also saves about 1,800 bytes of code space. (check-in: 3f5f60cd75 user: drh tags: omit-column-cache)
20:19
Fix the handling of sub-queries with LIMIT clauses by the optimization activated by compile-time symbol SQLITE_COUNTOFVIEW_OPTIMIZATION. (check-in: 21235d9a41 user: dan tags: trunk)
15:58
Fix the OP_SeekRowid opcode so that it has no type-change side-effects on the key register in P3. This fixes an obcure problem that arises when doing equi-joins between a table with a TEXT column against another table with an INTEGER PRIMARY KEY. The original problem was discovered when OSSFuzz created such a query and hit an assert() in OP_VerifyTabCol that was specifically designed to catch these kinds of errors at run-time. Test cases for this fix are in TH3. (check-in: fa94b49e02 user: drh tags: trunk)
Changes
Unified Diff Show Whitespace Changes Patch
Changes to src/select.c.
5491
5492
5493
5494
5495
5496
5497

5498
5499
5500
5501
5502
5503
5504
** Into this:
**
**    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

**   *  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;







>







5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
** Into this:
**
**    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;
5514
5515
5516
5517
5518
5519
5520

5521
5522
5523
5524
5525
5526
5527
  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 */
  if( pSub->pPrior==0 ) return 0;                   /* Must be a compound ry */
  do{
    if( pSub->op!=TK_ALL && pSub->pPrior ) return 0;  /* Must be UNION ALL */
    if( pSub->pWhere ) return 0;                      /* No WHERE clause */

    if( pSub->selFlags & SF_Aggregate ) return 0;     /* Not an aggregate */
    pSub = pSub->pPrior;                              /* Repeat over compound */
  }while( pSub );

  /* If we reach this point then it is OK to perform the transformation */

  db = pParse->db;







>







5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
  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 */
  if( pSub->pPrior==0 ) return 0;                   /* Must be a compound ry */
  do{
    if( pSub->op!=TK_ALL && pSub->pPrior ) return 0;  /* Must be UNION ALL */
    if( pSub->pWhere ) return 0;                      /* No WHERE clause */
    if( pSub->pLimit ) return 0;                      /* No LIMIT clause */
    if( pSub->selFlags & SF_Aggregate ) return 0;     /* Not an aggregate */
    pSub = pSub->pPrior;                              /* Repeat over compound */
  }while( pSub );

  /* If we reach this point then it is OK to perform the transformation */

  db = pParse->db;
5774
5775
5776
5777
5778
5779
5780










5781
5782
5783
5784
5785
5786
5787
      SELECTTRACE(0x100,pParse,p,("After constant propagation:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
#endif
  }else{
    SELECTTRACE(0x100,pParse,p,("Constant propagation not helpful\n"));
  }











  /* For each term in the FROM clause, do two things:
  ** (1) Authorized unreferenced tables
  ** (2) Generate code for all sub-queries
  */
  for(i=0; i<pTabList->nSrc; i++){
    struct SrcList_item *pItem = &pTabList->a[i];







>
>
>
>
>
>
>
>
>
>







5776
5777
5778
5779
5780
5781
5782
5783
5784
5785
5786
5787
5788
5789
5790
5791
5792
5793
5794
5795
5796
5797
5798
5799
      SELECTTRACE(0x100,pParse,p,("After constant propagation:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
#endif
  }else{
    SELECTTRACE(0x100,pParse,p,("Constant propagation not helpful\n"));
  }

#ifdef SQLITE_COUNTOFVIEW_OPTIMIZATION
  if( OptimizationEnabled(db, SQLITE_QueryFlattener|SQLITE_CountOfView)
   && countOfViewOptimization(pParse, p)
  ){
    if( db->mallocFailed ) goto select_end;
    pEList = p->pEList;
    pTabList = p->pSrc;
  }
#endif

  /* For each term in the FROM clause, do two things:
  ** (1) Authorized unreferenced tables
  ** (2) Generate code for all sub-queries
  */
  for(i=0; i<pTabList->nSrc; i++){
    struct SrcList_item *pItem = &pTabList->a[i];
5951
5952
5953
5954
5955
5956
5957
5958
5959
5960
5961
5962
5963
5964
5965
5966
5967
5968
5969
5970
5971
5972
5973
5974
  sDistinct.isTnct = (p->selFlags & SF_Distinct)!=0;

#if SELECTTRACE_ENABLED
  if( sqlite3SelectTrace & 0x400 ){
    SELECTTRACE(0x400,pParse,p,("After all FROM-clause analysis:\n"));
    sqlite3TreeViewSelect(0, p, 0);
  }
#endif

#ifdef SQLITE_COUNTOFVIEW_OPTIMIZATION
  if( OptimizationEnabled(db, SQLITE_QueryFlattener|SQLITE_CountOfView)
   && countOfViewOptimization(pParse, p)
  ){
    if( db->mallocFailed ) goto select_end;
    pEList = p->pEList;
    pTabList = p->pSrc;
  }
#endif

  /* If the query is DISTINCT with an ORDER BY but is not an aggregate, and 
  ** if the select-list is the same as the ORDER BY list, then this query
  ** can be rewritten as a GROUP BY. In other words, this:
  **
  **     SELECT DISTINCT xyz FROM ... ORDER BY xyz







<
<
<
<
<
<
<
<
<
<







5963
5964
5965
5966
5967
5968
5969










5970
5971
5972
5973
5974
5975
5976
  sDistinct.isTnct = (p->selFlags & SF_Distinct)!=0;

#if SELECTTRACE_ENABLED
  if( sqlite3SelectTrace & 0x400 ){
    SELECTTRACE(0x400,pParse,p,("After all FROM-clause analysis:\n"));
    sqlite3TreeViewSelect(0, p, 0);
  }










#endif

  /* If the query is DISTINCT with an ORDER BY but is not an aggregate, and 
  ** if the select-list is the same as the ORDER BY list, then this query
  ** can be rewritten as a GROUP BY. In other words, this:
  **
  **     SELECT DISTINCT xyz FROM ... ORDER BY xyz
Added test/countofview.test.
























































































>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
# 2018-08-04
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# 
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
source $testdir/malloc_common.tcl
set testprefix countofview

do_execsql_test 1.0 {
  CREATE TABLE t2(c);
  CREATE TABLE t3(f);

  INSERT INTO t2 VALUES(1), (2);
  INSERT INTO t3 VALUES(3);
}

do_execsql_test 1.1 {
  select c from t2 union all select f from t3 limit 1 offset 1
} {2}

do_execsql_test 1.2 {
  select count(*) from (
    select c from t2 union all select f from t3 limit 1 offset 1
  )
} {1}

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

finish_test