Date: Sun, 07 Aug 2022 20:06:21 +0000
To: "pgsql-sql@lists.postgresql.org" <pgsql-sql@lists.postgresql.org>
From: Adam Mackler <adam@mackler.email>
Reply-To: Adam Mackler <adam@mackler.email>
Subject: Possible bug (or at least unexpected behavior)
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Hi, forgive me if I should be posting this somewhere else.=C2=A0 I asked th=
e following question on stackoverflow, and the first response suggests a po=
ssible bug:

https://stackoverflow.com/questions/73261240/recursive-sql-function-returni=
ng-array-has-extra-elements-when-self-invocation-u#73261240

Briefly, given the following function:

    CREATE FUNCTION runs(input int[], output int[] DEFAULT '{}')
    RETURNS int[] AS $$
      SELECT
        CASE WHEN cardinality(input) =3D 0 THEN output
        ELSE runs(input[2:],
                  array_append(output, CASE
                    WHEN input[1] =3D 0 THEN 0
                    ELSE output[cardinality(output)] + input[1]
                  END)
                 )
        END
    $$ LANGUAGE SQL;

I expect the following invocation to return an array with the same number o=
f elements as the passed-in argument array:

    # select runs('{0,1,1,1,1,0,-1,-1,-1,0}');
                      runs
    ----------------------------------------
     {0,1,2,3,4,5,6,0,0,0,-1,-2,-3,-4,-5,0}
    (1 row)

which it does not with PostgreSQL version 14.4.  If it not a bug, then I wo=
uld be extremely interested in why it's returning an array with more elemen=
ts than the input array has.

Thanks in advance,
--
Adam Mackler