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https://issues.apache.org/jira/browse/CALCITE-6652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17893929#comment-17893929
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Julian Hyde commented on CALCITE-6652:
--------------------------------------
Why should this be decorrelator's job? The identity 'select x ... order by x
limit 1' → 'select min(x) ...' can apply to any query. Duplicate of
CALCITE-1317?
> 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();
> }
> @Test void testDecorrelateFetchOne2() {
> final String query = "SELECT deptno, (SELECT sal FROM emp where dept.deptno
> = emp.deptno order by emp.sal limit 1) FROM dept";
> sql(query).withRule(
> CoreRules.PROJECT_SUB_QUERY_TO_CORRELATE)
> .withLateDecorrelate(true)
> .check();
> }
> @Test void testDecorrelateFetchOne3() {
> final String query = "SELECT deptno, (SELECT sal FROM emp where dept.deptno
> = emp.deptno order by emp.sal desc limit 1) FROM dept";
> sql(query).withRule(
> CoreRules.PROJECT_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();
> }
> @Test void testDecorrelateFetchOne2() {
> final String query = "SELECT deptno, (SELECT SINGLE_VALUE(sal) FROM emp
> where dept.deptno = emp.deptno) FROM dept";
> sql(query).withRule(
> CoreRules.PROJECT_SUB_QUERY_TO_CORRELATE)
> .withLateDecorrelate(true)
> .check();
> }
> @Test void testDecorrelateFetchOne3() {
> final String query = "SELECT deptno, (SELECT max(sal) FROM emp where
> dept.deptno = emp.deptno) FROM dept";
> sql(query).withRule(
> CoreRules.PROJECT_SUB_QUERY_TO_CORRELATE)
> .withLateDecorrelate(true)
> .check();
> }{code}
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