Support for aggregate function with filter

[jimexist]

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A new challenge, to support aggregate function with filter. See Postgres manual

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Exactly like in the manual

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[Dandandan]

That would be a valuable feature @jimexist

[alamb]

@jimexist if you are proposing supporting this kind of syntax, then I think it is a reasonable idea.

SELECT
    count(*) AS unfiltered,
    count(*) FILTER (WHERE i < 5) AS filtered
FROM generate_series(1,10) AS s(i);
 unfiltered | filtered
------------+----------
         10 |        4
(1 row)

For anyone else who might read this ticket, You can express the same type of query using SQL that data fusion already supports via CASE, though it is much less beautiful. Something like:

$ seq 1 10 > /tmp/foo.csv
$ cargo run -p datafusion-cli

> CREATE EXTERNAL TABLE t(i double) STORED AS CSV LOCATION '/tmp/foo.csv';

> select * from t;
+----+
| i  |
+----+
| 1  |
| 2  |
| 3  |
| 4  |
| 5  |
| 6  |
| 7  |
| 8  |
| 9  |
| 10 |
+----+

>    select count(*) as unfiltered, sum(case when i < 5 then 1 else 0 end) as filtered from t;
+------------+----------+
| unfiltered | filtered |
+------------+----------+
| 10         | 4        |
+------------+----------+

[Dandandan]

@alamb yes, that's a great one - isn't that only feasible with SUM/MAX/MIN? I think primary use case would be COUNT or AVG

Edit: yeah or simulating count using SUM, as I am seeing in your example. You could do something in the same way for AVG of course if you are feeling creative :D

[kawadakk]

This feature has been implemented by #5868. Note that (afaik) you still need to select a SQL dialect supporting it.

[jayzhan211]

This feature has been implemented by #5868. Note that (afaik) you still need to select a SQL dialect supporting it.

It seems we can close this issue