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  1. MariaDB ColumnStore
  2. MCOL-4569 Queries with UNION ALL perform disproportionally badly
  3. MCOL-4589

Optimize out columns in a subquery involving a UNION which are not referenced in the outer select

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    Details

    • Type: Sub-Task
    • Status: Closed (View Workflow)
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 5.6.1
    • Component/s: Connector
    • Labels:
      None
    • Sprint:
      2021-4

      Description

      This task is similar to MCOL-4543, but for subqueries involving a UNION. I.e., If query Q1 is of the form:

      SELECT count(c2) FROM (SELECT * FROM t1 UNION ALL SELECT * FROM t1)q;
      

      Assuming t1 here contains 10 columns c1, c2, ... , c10. We build an ineffective RowGroup in ExeMgr of the form (1, c2_value1, 1, 1, 1, 1, 1, 1, 1, 1). The objective here is to remove all non-referenced columns from the end, until the first referenced column is encountered, i.e. trim down the RowGroup to (1, c2_value1).

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            Assignee:
            dleeyh Daniel Lee
            Reporter:
            tntnatbry Gagan Goel
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