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                              WORKLOG TASK
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TASK...........: Subqueries: Inside-out execution for non-semijoin materialized
		subqueries that are AND-parts of the WHERE
CREATION DATE..: Sun, 28 Feb 2010, 14:02
SUPERVISOR.....: Monty
IMPLEMENTOR....: 
COPIES TO......: Igor, Psergey, Timour
CATEGORY.......: Server-RawIdeaBin
TASK ID........: 92 (http://askmonty.org/worklog/?tid=92)
VERSION........: WorkLog-3.4
STATUS.........: Un-Assigned
PRIORITY.......: 60
WORKED HOURS...: 0
ESTIMATE.......: 0 (hours remain)
ORIG. ESTIMATE.: 0

PROGRESS NOTES:

-=-=(Psergey - Sun, 28 Feb 2010, 14:03)=-=-
Observers changed: Psergey,Igor,Timour



DESCRIPTION:

Consider the following case:

SELECT * FROM big_table 
WHERE oe IN (SELECT ie FROM table_with_few_groups
             WHERE ...
             GROUP BY group_col) AND ...

Here the best way to execute the query is:
  
  Materialize the subquery;
  # now run the join:
  for each record R1 in materialized table
    for each record R2 in big_table such that oe=R1
      pass R2 to output

Semi-join materialization supports such strategy with SJM-Scan strategy. This WL
entry is about adding support for such strategies for non-semijoin subqueries.


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