Re: [HACKERS] Query fails when SRFs are part of FROM clause (Commitid: 69f4b9c85f)

On Fri, Jan 27, 2017 at 5:28 AM, Rushabh Lathia <rushabh.lathia@gmail.com> wrote:

Consider the below test;

CREATE TABLE tab ( a int primary key);

SELECT  *

FROM pg_constraint pc,

CAST(CASE WHEN pc.contype IN ('f','u','p') THEN generate_series(1, array_upper(pc.conkey, 1)) ELSE NULL END AS int) AS position;

Above query is failing with "set-valued function called in context that cannot

accept a set". But if I remove the CASE from the query then it working just good.

Like:

SELECT  * 

FROM pg_constraint pc,

CAST(generate_series(1, array_upper(pc.conkey, 1)) AS int) AS position;

This started failing with 69f4b9c85f168ae006929eec44fc44d569e846b9. It seems

check_srf_call_placement() sets the hasTargetSRFs flag and but when the SRFs

at the rtable ofcourse this flag doesn't get set. It seems like missing something

their, but I might be completely wrong as not quire aware of this area.

I'm a bit surprised that your query actually works...and without delving into source code its hard to explain why it should/shouldn't or whether the recent SRF work was intended to impact it.

In any case the more idiomatic way of writing your query these days (since 9.4 came out) is:

SELECT *

FROM pg_constraint pc

LEFT JOIN LATERAL generate_series(1, case when contype in ('f','p','u') then array_upper(pc.conkey, 1) else 0 end) gs ON true;

generate_series is smart enough to return an empty set (instead of erroring out) when provided with (1,0) as arguments.

David J.