[jira] [Commented] (LENS-714) Replace dimension tables with subquery in Columnar Rewriter

["Sushil Mohanty (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LENS-714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14659489#comment-14659489 ] 

Sushil Mohanty commented on LENS-714:
-------------------------------------

rb entry : https://reviews.apache.org/r/37163/

> Replace dimension tables with subquery in Columnar Rewriter
> -----------------------------------------------------------
>
>                 Key: LENS-714
>                 URL: https://issues.apache.org/jira/browse/LENS-714
>             Project: Apache Lens
>          Issue Type: Improvement
>            Reporter: Sushil Mohanty
>            Assignee: Sushil Mohanty
>
> In order to optimise the JDBC sql queries, we can skip directly joining with the dimension tables. Instead we can create a subquery with only required column for a table used in the query. For eg. If column id and name are queried from  table dim1 the query can be rewritten as 
> ... inner join (select id,name from dim1) as d1 instead of ...inner join dim1 as d1. 
> For dimension tables with descent size this helps in improving performance to a great extent. Planning to add this in ColumnarRewriter so that columnar DBs can leverage this. 



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