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  1. MariaDB Server
  2. MDEV-28818

Eliminate derived tables having DISTINCT and/or UNION

Details

    • Task
    • Status: Open (View Workflow)
    • Major
    • Resolution: Unresolved
    • None
    • None
    • None

    Description

      MDEV-26278 only considers derived tables having GROUP BY expressions. But if a derived table has SELECT DISTINCT this can also be considered as if table has a unique key on selected fields, and so can be a subject to elimination:

      select t1.* from t1 left join  (select distinct a from t2) D on D.a=t1.a;

      Also MDEV-26278 does not implement elimination for derived tables with UNION, though it seems possible:

      select t1.* from t1 left join 
        (select distinct a from t2
      		 
         union
      		 
         select distinct a from t3) D 
      on D.a=t1.a;

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          relates to

          Task - A task that needs to be done. MDEV-26278 Table elimination does not work across derived tables

          • Critical - Crashes, loss of data, severe memory leak.
          • Closed

          Activity

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            oleg.smirnov Oleg Smirnov created issue -
            oleg.smirnov Oleg Smirnov made changes -
            Field Original Value New Value
            serg Sergei Golubchik made changes -
            Fix Version/s 10.11 [ 27614 ]
            Fix Version/s 10.10 [ 27530 ]
            ralf.gebhardt Ralf Gebhardt made changes -
            Fix Version/s 11.1 [ 28549 ]
            Fix Version/s 10.11 [ 27614 ]
            ralf.gebhardt Ralf Gebhardt made changes -
            Fix Version/s 11.3 [ 28565 ]
            Fix Version/s 11.1 [ 28549 ]
            serg Sergei Golubchik made changes -
            Fix Version/s 11.4 [ 29301 ]
            Fix Version/s 11.3 [ 28565 ]
            serg Sergei Golubchik made changes -
            Fix Version/s 11.5 [ 29506 ]
            Fix Version/s 11.4 [ 29301 ]
            serg Sergei Golubchik made changes -
            Fix Version/s 11.6 [ 29515 ]
            Fix Version/s 11.5 [ 29506 ]
            ralf.gebhardt Ralf Gebhardt made changes -
            Fix Version/s 11.6 [ 29515 ]

            People

              oleg.smirnov Oleg Smirnov
              oleg.smirnov Oleg Smirnov
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              Dates

                Created:
                Updated:

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