Vova Vysotskyi created DRILL-7421:
-------------------------------------
Summary: FILTER clause for aggregate functions is ignored
Key: DRILL-7421
URL: https://issues.apache.org/jira/browse/DRILL-7421
Project: Apache Drill
Issue Type: Bug
Affects Versions: 1.16.0
Reporter: Vova Vysotskyi
Fix For: Future
Drill ignores FILTER clause for aggregate functions.
The following query returns the wrong result:
{code:sql}
select count(*), count(employee_id) filter(where employee_id < 5) from
{code}
{noformat}
cp.`employee.json`;
+--------+--------+
| EXPR$0 | EXPR$1 |
+--------+--------+
| 1155 | 1155 |
+--------+--------+
{noformat}
Calcite already supports this feature (CALCITE-704) and as it is mentioned in
the Jira ticket, such syntax is allowed by SQL standard.
As a short solution, we should throw an exception for such queries that this
functionality is not supported.
As was mentioned in Calcite's Jira, some queries may be rewritten using switch
case:
{code:sql}
select count(*), count(case when employee_id < 5 then employee_id else null
end) from cp.`employee.json`;
{code}
It is possible to add functionality into Drill to rewrite filtered aggregate
calls in such a way, but some aggregate functions still would not be supported,
for example, {{count(*)}}.
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