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  1. MariaDB Server
  2. MDEV-2616

LP:858732 - Wrong result with semijoin + loosescan + comma join

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Details

    • Bug
    • Status: Closed (View Workflow)
    • Resolution: Fixed
    • None
    • None
    • None

    Description

      The following query

      SELECT * FROM t3 WHERE (f12) IN ( SELECT alias2.f12 FROM t1 AS alias1 , t2 AS alias2 , t1 WHERE alias1.f13 = 24 );

      returns more rows than are in t3 when executed with semijoin + loosescan.

      explain:

      id select_type table type possible_keys key key_len ref rows filtered Extra
      1 PRIMARY alias1 const PRIMARY PRIMARY 4 const 1 100.00 Using index
      1 PRIMARY alias2 index f12 f12 7 NULL 1 100.00 Using index; LooseScan
      1 PRIMARY t1 index NULL PRIMARY 4 NULL 2 100.00 Using index; FirstMatch(alias2); Using join buffer (flat, BNL join)
      1 PRIMARY t3 ALL NULL NULL NULL NULL 7 100.00 Using where; Using join buffer (flat, BNL join)

      explain extended:

      select `test`.`t3`.`f12` AS `f12` from `test`.`t1` `alias1` semi join (`test`.`t2` `alias2` join `test`.`t1`) join `test`.`t3` where ((`test`.`t3`.`f12` = `test`.`alias2`.`f12`))

      minimal optimizer switch:

      semijoin=ON,loosescan=ON

      full optimizer switch:

      index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,index_condition_pushdown=off,derived_merge=off,derived_with_keys=off,firstmatch=off,loosescan=on,materialization=off,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=off,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=off,semijoin_with_cache=off,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on

      bzr version-info:

      revision-id: <email address hidden>
      date: 2011-09-24 14:45:49 +0200
      build-date: 2011-09-25 11:24:23 +0300
      revno: 3194
      branch-nick: maria-5.3

      test case:

      --source include/have_innodb.inc
      CREATE TABLE t1 ( f13 int(11) NOT NULL , PRIMARY KEY (f13)) ENGINE=InnoDB;
      INSERT INTO t1 VALUES (16),(24);

      CREATE TABLE t2 ( f14 int(11) NOT NULL , f12 varchar(1) NOT NULL , KEY (f12,f14)) ENGINE=InnoDB;
      INSERT INTO t2 VALUES (6,'y');

      CREATE TABLE t3 ( f12 varchar(1) NOT NULL ) ENGINE=InnoDB;
      INSERT INTO t3 VALUES ('r'),('s'),('t'),('v'),('w'),('x'),('y');

      SET SESSION optimizer_switch='semijoin=ON,loosescan=ON';
      SELECT * FROM t3 WHERE (f12) IN ( SELECT alias2.f12 FROM t1 AS alias1 , t2 AS alias2 , t1 WHERE alias1.f13 = 24 );

      returns "y", "y". Expected just a single "y".

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            psergei Sergei Petrunia
            philipstoev Philip Stoev (Inactive)
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              Updated:
              Resolved:

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