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https://issues.apache.org/jira/browse/FLINK-4565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15696107#comment-15696107
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Nikolay Vasilishin commented on FLINK-4565:
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[~fhueske], I've finally opened the PR,
[https://github.com/apache/flink/pull/2870].
And what's about subqueries.
As I've seen above, there are couple of ways to implement it:
- create table with inner join somewhere at the beginning
- try to use calcite's IN operator, when constructing RexNode.
I tried to implement the second approach. It looks as it has to be
([example|https://github.com/NickolayVasilishin/flink/commit/792a10440eede233260d3b2157fbd93af9e3572f#diff-7c7c5dd5a5723b84b8d45424f04b2be5R68]).
In that case we need to [overload in
method|https://github.com/NickolayVasilishin/flink/commit/792a10440eede233260d3b2157fbd93af9e3572f#diff-04d1bca648d7ee47ab9ce787c8d944a6R108]
with Table argument, then somehow construct proper rex node in [toRexNode
method|https://github.com/NickolayVasilishin/flink/commit/792a10440eede233260d3b2157fbd93af9e3572f#diff-04d1bca648d7ee47ab9ce787c8d944a6R108]
(now it constructs not-working plan, I'll show it below). Then it will be
passed to
[CodeGenerator|https://github.com/NickolayVasilishin/flink/commit/792a10440eede233260d3b2157fbd93af9e3572f#diff-c0ee691580cf6752e6cb186ca4f0260dR980],
where I have to implement visitSubquery method. Actually, it's not hard to
generate code for all subquery's nodes, but I don't know, what code should be
ganarated to link subquery with the rest query.
RexNode constructed whis way has this logical plan:
{noformat}
LogicalFilter(condition=[IN(IN($2, {
LogicalProject(c=[$2])
LogicalFilter(condition=[=($1, 6)])
LogicalTableScan(table=[[_DataSetTable_0]])
}))])
LogicalTableScan(table=[[_DataSetTable_0]])
{noformat}
There is duplicating IN call.
Logical plan generating for similar query in SQL API looks like this:
{noformat}
LogicalProject(a=[$0], c=[$2])
LogicalJoin(condition=[=($1, $3)], joinType=[inner])
LogicalTableScan(table=[[_DataSetTable_0]])
LogicalAggregate(group=[{0}])
LogicalProject(b=[$1])
LogicalFilter(condition=[AND(>=($1, 6), <=($1, 9))])
LogicalTableScan(table=[[_DataSetTable_0]])
{noformat}
So, it's implemented via the first approach.
In the first approach it's not clear for me where we will get reference on
first (left) table, as we invoke IN method on expressions like 'column. But I
didn't thought about it well yet.
> Support for SQL IN operator
> ---------------------------
>
> Key: FLINK-4565
> URL: https://issues.apache.org/jira/browse/FLINK-4565
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Reporter: Timo Walther
> Assignee: Nikolay Vasilishin
>
> It seems that Flink SQL supports the uncorrelated sub-query IN operator. But
> it should also be available in the Table API and tested.
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