[teiid-issues] [JBoss JIRA] (TEIID-4498) Generalize subquery batch processing

[Steven Hawkins (Jira)]

     [ https://issues.jboss.org/browse/TEIID-4498?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steven Hawkins updated TEIID-4498:
----------------------------------
    Fix Version/s: 12.0
                       (was: 12.x)


I'll see if this can be addressed in 12.0.

The first step is to generalize the unnesting that we do for subqueries in the where clause to other locations.

For situations where that is not possible we can consider an optimization that would create a base common table, and common tables for each of the subqueries (similar to the logic that raised criteria in the xml processing logic).

select (select ... ), (select ...), a, b ... from ...

would become:

with base as (select ... a, b ... from ...)
         sub1 as (select ... from ..., base where ... col = base.col, ...)
         sub2 as (select ... from ..., base where ... col = base.col, ...)
select (select ... from sub1 where col = base.col), (select ... from sub2 where col = base.col) ... from base

which means that after loading the base, we'll use that to drive the load of each of the sub query tables, 

> Generalize subquery batch processing
> ------------------------------------
>
>                 Key: TEIID-4498
>                 URL: https://issues.jboss.org/browse/TEIID-4498
>             Project: Teiid
>          Issue Type: Enhancement
>          Components: Query Engine
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>            Priority: Major
>             Fix For: 12.0
>
>
> For subqueries that cannot be unnested, but can be modified to project their correlation, we should have at least batch processing rather than the row by row default.



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