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https://issues.apache.org/jira/browse/CALCITE-3764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17028277#comment-17028277
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Rui Wang commented on CALCITE-3764:
-----------------------------------
However, I am not sure if the proposed solution is correct.
Converting to "WHERE b IS NOT TRUE" is correct only for the special case "THEN
NULL ELSE 1 END".
Think about a general case:
{code:sql}
SELECT AGG_FUNCTION(CASE WHEN b THEN result_1 ELSE result_2 END) FROM t
{code}
basically for an arbitrary aggregation function, FILTER clause shouldn't be
used and CASE should be preserved. Because we cannot always ignore result_1.
For example,
{code:sql}
SELECT SUM(CASE WHEN b THEN col_1 ELSE col_2 END) FROM t
{code}
cannot be converted to
{code:sql}
SELECT SUM(col_2) FILTER (WHERE b IS NOT TRUE) FROM t
{code}
Unless this jira tries to address "COUNT(CASE WHEN b THEN NULL ELSE 1 END)" as
a special case, otherwise the right resolution is to not convert to FILTER if
there is more than one THEN.
I can try to open a PR for it.
> AggregateCaseToFilterRule handles NULL values correctly
> -------------------------------------------------------
>
> Key: CALCITE-3764
> URL: https://issues.apache.org/jira/browse/CALCITE-3764
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Priority: Major
>
> {{AggregateCaseToFilterRule}} handles NULL values correctly. It converts
> {code:sql}
> SELECT COUNT(CASE WHEN b THEN NULL ELSE 1 END) FROM t
> {code}
> to
> {code:sql}
> SELECT COUNT(*) FILTER (WHERE b IS FALSE) FROM t
> {code}
> which fails to count rows where {{b}} is UNKNOWN, so it should convert to
> {code:sql}
> SELECT COUNT(*) FILTER (WHERE b IS NOT TRUE) FROM t
> {code}
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