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  1. MDEV-429

Extra field 'Using filesort' in EXPLAIN vs 'Using where; Using filesort' in SHOW EXPLAIN on a query with HAVING and ORDER BY

    Details

    • Type: Bug
    • Status: Closed
    • Priority: Minor
    • Resolution: Won't Fix
    • Affects versions: None
    • Fix versions: 10.0.0
    • Components: None
    • Labels:
      None
    • Sprint:

      Description

      EXPLAIN SELECT alias1.b FROM t1 AS alias1 LEFT JOIN t1 AS alias2 ON (alias2.b = alias1.a)  
      WHERE EXISTS ( SELECT * FROM t1 WHERE a <= alias2.a )  
      HAVING alias1.b > 10 ORDER BY alias1.b;
      id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
      1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	9	Using filesort
      1	PRIMARY	alias2	ref	b	b	5	test.alias1.a	2	Using where
      2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	9	Using where
      #---------------
      # SHOW EXPLAIN output:
      id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
      1	PRIMARY	alias1	ALL	NULL	NULL	NULL	NULL	9	Using where; Using filesort
      1	PRIMARY	alias2	ref	b	b	5	test.alias1.a	2	Using where
      2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	9	Using where
      

      bzr version-info

      revision-id: psergey@askmonty.org-20120801115152-qgxtqd0a5vlqrrhx
      date: 2012-08-01 15:51:52 +0400
      build-date: 2012-08-02 16:12:26 +0300
      revno: 3461
      

      Default optimizer_switch:

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

      Test case:

      CREATE TABLE t1 (a INT, b INT, KEY(b)) ENGINE=MyISAM;
      INSERT INTO t1 VALUES 
      (0,4),(8,6),(1,3),(8,5),(9,3),(2,4),(6,2),(1,9),(6,3);
      
      	
      let $query =
      SELECT alias1.b FROM t1 AS alias1 LEFT JOIN t1 AS alias2 ON (alias2.b = alias1.a)  
      WHERE EXISTS ( SELECT * FROM t1 WHERE a <= alias2.a )  
      HAVING alias1.b > 10 ORDER BY alias1.b;
      
      
      eval EXPLAIN $query;
      --echo #---------------
      --echo # SHOW EXPLAIN output:
      
      --connect (con1,localhost,root,,)
      --let $con_id = `SELECT CONNECTION_ID()`
      
      --let $trials = 50
      
      --disable_query_log
      
      while ($trials)
      {
        --dec $trials
        --let $run = 1000
      
        --send_eval $query
      
        --connection default
        while ($run)
        {
          --error 0,1932
          eval SHOW EXPLAIN FOR $con_id;
          --dec $run
          if (!$mysql_errno)
          {
            --let $run = 0
            --let $trials = 0
            --let $found = 1
          }
        }
      
        --disable_result_log
        --connection con1
        --reap
        --enable_result_log
      
      }
      
      if (!$found)
      {
        --echo ########### Could not catch the query by SHOW EXPLAIN, try again  #############
      }
      
      DROP TABLE t1;
      
      

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              • Assignee:
                psergey Sergei Petrunia
                Reporter:
                elenst Elena Stepanova
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                  Updated:
                  Resolved:

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