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Comment:When flattening UNION ALL subqueries into a join query, ensure that separate cursor numbers are used for each segment of the newly flattened query.
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SHA3-256: c510377b0b052e400f2ee4f20220b61cdf74ee44b9bb9e6490787c88dd4c55aa
User & Date: dan 2020-12-18 16:13:39
Context
2020-12-18
18:04
Fix for the previous fix in the case where a UNION ALL sub-query is joined against some other compound query. (Closed-Leaf check-in: 63c5cfb9 user: dan tags: union-all-flattener)
16:13
When flattening UNION ALL subqueries into a join query, ensure that separate cursor numbers are used for each segment of the newly flattened query. (check-in: c510377b user: dan tags: union-all-flattener)
2020-12-17
17:17
Fix a part of the header comment for flattenSubquery(). (check-in: dc0937ce user: dan tags: union-all-flattener)
Changes
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Changes to src/select.c.

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  w.xSelectCallback = sqlite3SelectWalkNoop;
  w.u.pSrcItem = pSrcItem;
  pSrcItem->colUsed = 0;
  sqlite3WalkSelect(&w, pSelect);
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */

















































































#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
** This routine attempts to flatten subqueries as a performance optimization.
** This routine returns 1 if it makes changes and 0 if no flattening occurs.
**
** To understand the concept of flattening, consider the following
** query:







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  w.xSelectCallback = sqlite3SelectWalkNoop;
  w.u.pSrcItem = pSrcItem;
  pSrcItem->colUsed = 0;
  sqlite3WalkSelect(&w, pSelect);
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */

#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
** Assign new cursor numbers to each of the items in pSrc. For each
** new cursor number assigned, set an entry in the aCsrMap[] array 
** to map the old cursor number to the new:
**
**     aCsrMap[iOld] = iNew;
**
** The array is guaranteed by the caller to be large enough for all
** existing cursor numbers in pSrc.
**
** If pSrc contains any sub-selects, call this routine recursively
** on the FROM clause of each such sub-select, with iExcept set to -1.
*/
static void srclistRenumberCursors(
  Parse *pParse,                  /* Parse context */
  int *aCsrMap,                   /* Array to store cursor mappings in */
  SrcList *pSrc,                  /* FROM clause to renumber */
  int iExcept                     /* FROM clause item to skip */
){
  int i;
  struct SrcList_item *pItem;
  for(i=0, pItem=pSrc->a; i<pSrc->nSrc; i++, pItem++){
    if( i!=iExcept ){
      int iNew = pParse->nTab++;
      aCsrMap[pItem->iCursor] = iNew;
      pItem->iCursor = iNew;
      if( pItem->pSelect ){
        srclistRenumberCursors(pParse, aCsrMap, pItem->pSelect->pSrc, -1);
      }
    }
  }
}

/*
** Expression walker callback used by renumberCursors() to update
** Expr objects to match newly assigned cursor numbers.
*/
static int renumberCursorsCb(Walker *pWalker, Expr *pExpr){
  int *aCsrMap = pWalker->u.aiCol;
  if( pExpr->op==TK_COLUMN && aCsrMap[pExpr->iTable] ){
    pExpr->iTable = aCsrMap[pExpr->iTable];
  }
  return WRC_Continue;
}

/*
** Assign a new cursor number to each cursor in the FROM clause (Select.pSrc)
** of the SELECT statement passed as the second argument, and to each 
** cursor in the FROM clause of any FROM clause sub-selects, recursively.
** Except, do not assign a new cursor number to the iExcept'th element in
** the FROM clause of (*p). Update all expressions and other references 
** to refer to the new cursor numbers.
**
** Argument aCsrMap is an array that may be used for temporary working
** space. Two guarantees are made by the caller:
**
**   * the array is larger than the largest cursor number used within the
**     select statement passed as an argument, and
**
**   * the array entries for all cursor numbers that do *not* appear in 
**     FROM clauses of the select statement as described above are 
**     initialized to zero.
*/
static void renumberCursors(
  Parse *pParse,                  /* Parse context */
  Select *p,                      /* Select to renumber cursors within */
  int iExcept,                    /* FROM clause item to skip */
  int *aCsrMap                    /* Working space */
){
  Walker w;
  srclistRenumberCursors(pParse, aCsrMap, p->pSrc, iExcept);
  memset(&w, 0, sizeof(w));
  w.u.aiCol = aCsrMap;
  w.xExprCallback = renumberCursorsCb;
  w.xSelectCallback = sqlite3SelectWalkNoop;
  sqlite3WalkSelect(&w, p);
}
#endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */

#if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
/*
** This routine attempts to flatten subqueries as a performance optimization.
** This routine returns 1 if it makes changes and 0 if no flattening occurs.
**
** To understand the concept of flattening, consider the following
** query:
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  int iNewParent = -1;/* Replacement table for iParent */
  int isLeftJoin = 0; /* True if pSub is the right side of a LEFT JOIN */    
  int i;              /* Loop counter */
  Expr *pWhere;                    /* The WHERE clause */
  struct SrcList_item *pSubitem;   /* The subquery */
  sqlite3 *db = pParse->db;
  Walker w;                        /* Walker to persist agginfo data */


  /* Check to see if flattening is permitted.  Return 0 if not.
  */
  assert( p!=0 );
  assert( p->pPrior==0 );
  if( OptimizationDisabled(db, SQLITE_QueryFlattener) ) return 0;
  pSrc = p->pSrc;







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  int iNewParent = -1;/* Replacement table for iParent */
  int isLeftJoin = 0; /* True if pSub is the right side of a LEFT JOIN */    
  int i;              /* Loop counter */
  Expr *pWhere;                    /* The WHERE clause */
  struct SrcList_item *pSubitem;   /* The subquery */
  sqlite3 *db = pParse->db;
  Walker w;                        /* Walker to persist agginfo data */
  int *aCsrMap = 0;

  /* Check to see if flattening is permitted.  Return 0 if not.
  */
  assert( p!=0 );
  assert( p->pPrior==0 );
  if( OptimizationDisabled(db, SQLITE_QueryFlattener) ) return 0;
  pSrc = p->pSrc;
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      for(ii=0; ii<p->pOrderBy->nExpr; ii++){
        if( p->pOrderBy->a[ii].u.x.iOrderByCol==0 ) return 0;
      }
    }

    /* Restriction (23) */
    if( (p->selFlags & SF_Recursive) ) return 0;




  }

  /***** If we reach this point, flattening is permitted. *****/
  SELECTTRACE(1,pParse,p,("flatten %u.%p from term %d\n",
                   pSub->selId, pSub, iFrom));

  /* Authorize the subquery */







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      for(ii=0; ii<p->pOrderBy->nExpr; ii++){
        if( p->pOrderBy->a[ii].u.x.iOrderByCol==0 ) return 0;
      }
    }

    /* Restriction (23) */
    if( (p->selFlags & SF_Recursive) ) return 0;

    if( pSrc->nSrc>1 ){
      aCsrMap = sqlite3DbMallocZero(db, pParse->nTab*sizeof(int));
    }
  }

  /***** If we reach this point, flattening is permitted. *****/
  SELECTTRACE(1,pParse,p,("flatten %u.%p from term %d\n",
                   pSub->selId, pSub, iFrom));

  /* Authorize the subquery */
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    p->pLimit = pLimit;
    p->pOrderBy = pOrderBy;
    p->op = TK_ALL;
    pSubitem->pTab = pItemTab;
    if( pNew==0 ){
      p->pPrior = pPrior;
    }else{



      pNew->pPrior = pPrior;
      if( pPrior ) pPrior->pNext = pNew;
      pNew->pNext = p;
      p->pPrior = pNew;
      SELECTTRACE(2,pParse,p,("compound-subquery flattener"
                              " creates %u as peer\n",pNew->selId));
    }
    assert( pSubitem->pSelect==0 );


    if( db->mallocFailed ){
      pSubitem->pSelect = pSub1;
      return 1;
    }
  }

  /* Defer deleting the Table object associated with the
  ** subquery until code generation is
  ** complete, since there may still exist Expr.pTab entries that
  ** refer to the subquery even after flattening.  Ticket #3346.
  **







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    p->pLimit = pLimit;
    p->pOrderBy = pOrderBy;
    p->op = TK_ALL;
    pSubitem->pTab = pItemTab;
    if( pNew==0 ){
      p->pPrior = pPrior;
    }else{
      if( aCsrMap && db->mallocFailed==0 ){
        renumberCursors(pParse, pNew, iFrom, aCsrMap);
      }
      pNew->pPrior = pPrior;
      if( pPrior ) pPrior->pNext = pNew;
      pNew->pNext = p;
      p->pPrior = pNew;
      SELECTTRACE(2,pParse,p,("compound-subquery flattener"
                              " creates %u as peer\n",pNew->selId));
    }
    assert( pSubitem->pSelect==0 );
  }
  sqlite3DbFree(db, aCsrMap);
  if( db->mallocFailed ){
    pSubitem->pSelect = pSub1;
    return 1;

  }

  /* Defer deleting the Table object associated with the
  ** subquery until code generation is
  ** complete, since there may still exist Expr.pTab entries that
  ** refer to the subquery even after flattening.  Ticket #3346.
  **

Changes to test/unionall.test.

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  SELECT * FROM t1, t2 WHERE x=k ORDER BY k,v||''
} {
  2 two   2 ii
  2 TWO   2 ii 
  3 three 3 iii 
  3 THREE 3 iii 
}

































finish_test







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  SELECT * FROM t1, t2 WHERE x=k ORDER BY k,v||''
} {
  2 two   2 ii
  2 TWO   2 ii 
  3 three 3 iii 
  3 THREE 3 iii 
}
do_execsql_test 2.2.9a {
  SELECT * FROM t1, t2 ORDER BY +k
} {
  1 one 2 ii 1 ONE 2 ii 2 two 2 ii 
  2 TWO 2 ii 3 three 2 ii 3 THREE 2 ii 
  
  1 one 3 iii 1 ONE 3 iii 2 two 3 iii 
  2 TWO 3 iii 3 three 3 iii 3 THREE 3 iii 

  1 one 4 iv 1 ONE 4 iv 2 two 4 iv 
  2 TWO 4 iv 3 three 4 iv 3 THREE 4 iv 

  1 one 5 v 1 ONE 5 v 2 two 5 v 
  2 TWO 5 v 3 three 5 v 3 THREE 5 v
}

do_execsql_test 2.2.9b {
  SELECT * FROM t1, t2 ORDER BY k
} {
  1 one 2 ii 1 ONE 2 ii 2 two 2 ii 
  2 TWO 2 ii 3 three 2 ii 3 THREE 2 ii 
  
  1 one 3 iii 1 ONE 3 iii 2 two 3 iii 
  2 TWO 3 iii 3 three 3 iii 3 THREE 3 iii 

  1 one 4 iv 1 ONE 4 iv 2 two 4 iv 
  2 TWO 4 iv 3 three 4 iv 3 THREE 4 iv 

  1 one 5 v 1 ONE 5 v 2 two 5 v 
  2 TWO 5 v 3 three 5 v 3 THREE 5 v
}


finish_test

Changes to test/unionallfault.test.

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faultsim_save_and_close


do_faultsim_test 1 -faults oom-t* -prep {
  faultsim_restore_and_reopen
} -body {
  execsql {
    SELECT * FROM (
      SELECT x FROM t1 UNION ALL SELECT y FROM t1
    )
  }
} -test {
  faultsim_test_result {0 {}}
}

finish_test







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faultsim_save_and_close


do_faultsim_test 1 -faults oom-t* -prep {
  faultsim_restore_and_reopen
} -body {
  execsql {
    SELECT * FROM t1, (
      SELECT x FROM t1 UNION ALL SELECT y FROM t1
    ), t3
  }
} -test {
  faultsim_test_result {0 {}}
}

finish_test