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Overview
Comment:Fix a problem causing the planner to generate sub-optimal plans for some queries that use recursive WITH sub-queries with LIMIT clauses.
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SHA1: 053a149cc8244a7f85137129cfcb8622efe90306
User & Date: dan 2016-12-16 15:05:40
Context
2016-12-16
18:14
Built-in PRAGMA statements without side-effects can be invoked as table-valued functions by prefixing their name with "pragma_". check-in: d66ec5cf user: drh tags: trunk
15:57
Merge recent trunk enhancements. check-in: 74a0ca1f user: drh tags: est_count_pragma
15:05
Fix a problem causing the planner to generate sub-optimal plans for some queries that use recursive WITH sub-queries with LIMIT clauses. check-in: 053a149c user: dan tags: trunk
01:00
All temp.sqlite_master to be used as an alias for sqlite_temp_master. check-in: 8d646905 user: drh tags: trunk
Changes
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Changes to src/select.c.

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  int regLimit, regOffset;      /* Registers used by LIMIT and OFFSET */

  /* Obtain authorization to do a recursive query */
  if( sqlite3AuthCheck(pParse, SQLITE_RECURSIVE, 0, 0, 0) ) return;

  /* Process the LIMIT and OFFSET clauses, if they exist */
  addrBreak = sqlite3VdbeMakeLabel(v);

  computeLimitRegisters(pParse, p, addrBreak);
  pLimit = p->pLimit;
  pOffset = p->pOffset;
  regLimit = p->iLimit;
  regOffset = p->iOffset;
  p->pLimit = p->pOffset = 0;
  p->iLimit = p->iOffset = 0;
................................................................................
  if( pDest->eDest==SRT_EphemTab ){
    sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pDest->iSDParm, pEList->nExpr);
  }

  /* Set the limiter.
  */
  iEnd = sqlite3VdbeMakeLabel(v);

  p->nSelectRow = 320;  /* 4 billion rows */

  computeLimitRegisters(pParse, p, iEnd);
  if( p->iLimit==0 && sSort.addrSortIndex>=0 ){
    sqlite3VdbeChangeOpcode(v, sSort.addrSortIndex, OP_SorterOpen);
    sSort.sortFlags |= SORTFLAG_UseSorter;
  }

  /* Open an ephemeral index to use for the distinct set.







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  int regLimit, regOffset;      /* Registers used by LIMIT and OFFSET */

  /* Obtain authorization to do a recursive query */
  if( sqlite3AuthCheck(pParse, SQLITE_RECURSIVE, 0, 0, 0) ) return;

  /* Process the LIMIT and OFFSET clauses, if they exist */
  addrBreak = sqlite3VdbeMakeLabel(v);
  p->nSelectRow = 320;  /* 4 billion rows */
  computeLimitRegisters(pParse, p, addrBreak);
  pLimit = p->pLimit;
  pOffset = p->pOffset;
  regLimit = p->iLimit;
  regOffset = p->iOffset;
  p->pLimit = p->pOffset = 0;
  p->iLimit = p->iOffset = 0;
................................................................................
  if( pDest->eDest==SRT_EphemTab ){
    sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pDest->iSDParm, pEList->nExpr);
  }

  /* Set the limiter.
  */
  iEnd = sqlite3VdbeMakeLabel(v);
  if( (p->selFlags & SF_FixedLimit)==0 ){
    p->nSelectRow = 320;  /* 4 billion rows */
  }
  computeLimitRegisters(pParse, p, iEnd);
  if( p->iLimit==0 && sSort.addrSortIndex>=0 ){
    sqlite3VdbeChangeOpcode(v, sSort.addrSortIndex, OP_SorterOpen);
    sSort.sortFlags |= SORTFLAG_UseSorter;
  }

  /* Open an ephemeral index to use for the distinct set.

Changes to test/with3.test.

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  CREATE TABLE t1(x);
  WITH
    x1(a) AS (values(100))
  INSERT INTO t1(x)
    SELECT * FROM (WITH x2(y) AS (SELECT * FROM x1) SELECT y+a FROM x1, x2);
  SELECT * FROM t1;
} {200}

























































finish_test








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  CREATE TABLE t1(x);
  WITH
    x1(a) AS (values(100))
  INSERT INTO t1(x)
    SELECT * FROM (WITH x2(y) AS (SELECT * FROM x1) SELECT y+a FROM x1, x2);
  SELECT * FROM t1;
} {200}

#-------------------------------------------------------------------------
# Test that the planner notices LIMIT clauses on recursive WITH queries.
#

ifcapable analyze {
  do_execsql_test 3.1.1 {
    CREATE TABLE y1(a, b);
    CREATE INDEX y1a ON y1(a);

    WITH cnt(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM cnt LIMIT 1000)
      INSERT INTO y1 SELECT i%10, i FROM cnt;
    ANALYZE;

  }

  do_eqp_test 3.1.2 {
    WITH cnt(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM cnt LIMIT 1)
    SELECT * FROM cnt, y1 WHERE i=a
  } {
    3 0 0 {SCAN TABLE cnt} 
    1 0 0 {COMPOUND SUBQUERIES 0 AND 0 (UNION ALL)}
    0 0 0 {SCAN SUBQUERY 1} 
    0 1 1 {SEARCH TABLE y1 USING INDEX y1a (a=?)}
  }

  do_eqp_test 3.1.3 {
    WITH cnt(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM cnt LIMIT 1000000)
    SELECT * FROM cnt, y1 WHERE i=a
  } {
    3 0 0 {SCAN TABLE cnt} 
    1 0 0 {COMPOUND SUBQUERIES 0 AND 0 (UNION ALL)}
    0 0 1 {SCAN TABLE y1} 
    0 1 0 {SEARCH SUBQUERY 1 USING AUTOMATIC COVERING INDEX (i=?)}
  }
}

do_execsql_test 3.2.1 {
  CREATE TABLE w1(pk INTEGER PRIMARY KEY, x INTEGER);
  CREATE TABLE w2(pk INTEGER PRIMARY KEY);
}

do_eqp_test 3.2.2 {
  WITH RECURSIVE c(w,id) AS (SELECT 0, (SELECT pk FROM w2 LIMIT 1)
     UNION ALL SELECT c.w + 1, x FROM w1, c LIMIT 1)
     SELECT * FROM c, w2, w1
     WHERE c.id=w2.pk AND c.id=w1.pk;
} {
  2 0 0 {EXECUTE SCALAR SUBQUERY 3} 
  3 0 0 {SCAN TABLE w2} 
  4 0 0 {SCAN TABLE w1}
  4 1 1 {SCAN TABLE c} 
  1 0 0 {COMPOUND SUBQUERIES 0 AND 0 (UNION ALL)} 0 0 0 {SCAN SUBQUERY 1}
  0 1 1 {SEARCH TABLE w2 USING INTEGER PRIMARY KEY (rowid=?)} 
  0 2 2 {SEARCH TABLE w1 USING INTEGER PRIMARY KEY (rowid=?)}
}

finish_test