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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Correctly initialize the iSelectId of FROM clause terms that are a self join of a reused materialized subquery. Without this, the EXPLAIN QUERY PLAN output for the query will identify the subquery using the uninitialized (and arbitrary) iSelectId.
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SHA3-256: 43c9ae371f6250fee98a7c4011726eff8ad37f5a97add4f490ac3a2dd501a0d2
User & Date: drh 2017-05-29 13:09:24
Context
2017-05-29
14:26
Optimizations to the Walker object and its methods to make the code a little smaller and to help it run a little faster. check-in: 6854a34e user: drh tags: trunk
13:09
Correctly initialize the iSelectId of FROM clause terms that are a self join of a reused materialized subquery. Without this, the EXPLAIN QUERY PLAN output for the query will identify the subquery using the uninitialized (and arbitrary) iSelectId. check-in: 43c9ae37 user: drh tags: trunk
03:48
Improve shell help text for the '.open' command. check-in: 7cc940a9 user: mistachkin tags: trunk
Changes
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Changes to src/select.c.

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        VdbeComment((v, "materialize \"%s\"", pItem->pTab->zName));
      }else{
        VdbeNoopComment((v, "materialize \"%s\"", pItem->pTab->zName));
      }
      pPrior = isSelfJoinView(pTabList, pItem);
      if( pPrior ){
        sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pPrior->iCursor);

      }else{
        sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
        explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
        sqlite3Select(pParse, pSub, &dest);
      }
      pItem->pTab->nRowLogEst = pSub->nSelectRow;
      if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);







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        VdbeComment((v, "materialize \"%s\"", pItem->pTab->zName));
      }else{
        VdbeNoopComment((v, "materialize \"%s\"", pItem->pTab->zName));
      }
      pPrior = isSelfJoinView(pTabList, pItem);
      if( pPrior ){
        sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pPrior->iCursor);
        explainSetInteger(pItem->iSelectId, pPrior->iSelectId);
      }else{
        sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
        explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
        sqlite3Select(pParse, pSub, &dest);
      }
      pItem->pTab->nRowLogEst = pSub->nSelectRow;
      if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);

Changes to test/with1.test.

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  WITH xyz(x) AS (
    SELECT printf('%d', 5) * NULL
    UNION SELECT round(1<1+x) 
    FROM xyz ORDER BY 1
  )
  SELECT 1 FROM xyz;
} 1
















finish_test







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  WITH xyz(x) AS (
    SELECT printf('%d', 5) * NULL
    UNION SELECT round(1<1+x) 
    FROM xyz ORDER BY 1
  )
  SELECT 1 FROM xyz;
} 1

# EXPLAIN QUERY PLAN on a self-join of a CTE
#
do_execsql_test 19.1 {
  DROP TABLE IF EXISTS t1;
  CREATE TABLE t1(x);
  EXPLAIN QUERY PLAN
  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;
} {0 0 0 {SCAN SUBQUERY 1} 0 1 1 {SCAN SUBQUERY 1}}



finish_test