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https://issues.apache.org/jira/browse/CALCITE-5193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17866241#comment-17866241
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Viggo Chen commented on CALCITE-5193:
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[~Chunwei Lei] It is intuitive to pushdown `COALESCE(a.pt, b.pt)='20220601'` as
`pt='20220601'` filter to each input.
But how do we abstractly judge whether a filter condition can be pushed down?
I have a preliminary idea, but I'm not sure if it's correct. For left input,
replace all field from right input as null to create a new filter to pushdown.
And the same applies to the right side.
> Push filter whose conditions include join keys and are composed by OR into
> inputs of full join
> ----------------------------------------------------------------------------------------------
>
> Key: CALCITE-5193
> URL: https://issues.apache.org/jira/browse/CALCITE-5193
> Project: Calcite
> Issue Type: Improvement
> Reporter: Chunwei Lei
> Priority: Major
>
> For example,
> {code:sql}
> select * from a full join b on a.id=b.id where a.id=1 or b.id=2;
> {code}
> can be transformed to
> {code:sql}
> select * from
> (select * from a where id=1 or id=2) a
> full join
> (select * from b where id=1 or id=2) b
> on a.id=b.id;
> {code}
> If {{a}} and {{b}} are both partitioned tables and id is the partition key,
> we can do partition pruning with this transformation, which is a big
> improvement.
> This improvement is inspired by the query
> {code:java}
> select * from a full join b on a.id=b.id and a.pt=b.pt where COALESCE(a.pt,
> b.pt)='20220601';
> {code}
> which costs a lot due to it scans all partitions in table {{a}} and {{b}}.
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