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https://issues.apache.org/jira/browse/CALCITE-6652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17903857#comment-17903857
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suibianwanwan commented on CALCITE-6652:
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Also, for the case where the order key has more than one value, I inferred a
conversion.
For case:
{code:java}
SELECT dname FROM dept WHERE 2000 > (SELECT sal FROM "scott".emp where
dept.deptno = emp.deptno ORDER BY year(hiredate), sal limit 1); {code}
We optimize for
{code:java}
select deptno from dept join (SELECT sal1 from (SELECT first_value(sal) over
(partition by emp.deptno order by year(hiredate), emp.sal) as sal1, deptno)
group by deptno where sal1 < 1000) {code}
Rewrite logical:
{code:java}
// Rewrite logic:
//
// If sorted without offset and fetch = 1, rewrite the sort to be
// Aggregate(group=(corVar), agg=[any_value(field))
// project(first_value(field) over (partition by corVar order by (sort
collation)))
// originInput{code}
This seems to be a generic optimization for decorrelate containing sorting. But
unfortunately, I haven't seen proof of a similar conversion anywhere.
> RelDecorrelator can't decorrelate query with limit 1
> ----------------------------------------------------
>
> Key: CALCITE-6652
> URL: https://issues.apache.org/jira/browse/CALCITE-6652
> Project: Calcite
> Issue Type: Bug
> Reporter: suibianwanwan
> Assignee: suibianwanwan
> Priority: Major
>
> The following query can't decorrelate by RelDecorrelate:
> {code:java}
> @Test void testDecorrelateFetchOne1() {
> final String query = "SELECT deptno FROM dept WHERE\n" +
> "1000 > (SELECT sal FROM emp WHERE dept.deptno = emp.deptno order by
> emp.sal limit 1)";
> sql(query).withRule(
> CoreRules.FILTER_SUB_QUERY_TO_CORRELATE)
> .withLateDecorrelate(true)
> .check();
> }{code}
> is equivalent to the following query, and the following query can be
> decorrelated into a join, so we can do some appropriate conversions in
> RelDecorrelate:
> {code:java}
> @Test void testDecorrelateFetchOne1() {
> final String query = "SELECT deptno FROM dept WHERE\n" +
> "1000 > (SELECT min(sal) FROM emp WHERE dept.deptno = emp.deptno)";
> sql(query).withRule(
> CoreRules.FILTER_SUB_QUERY_TO_CORRELATE)
> .withLateDecorrelate(true)
> .check();
> }{code}
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