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Subject: BUG #19558: User-defined prefix operators "|" and "->" no longer
 parse in 19beta2 (SQL/PGQ grammar change)
To: pgsql-bugs@lists.postgresql.org
From: PG Bug reporting form <noreply@postgresql.org>
Cc: pierre@senellart.com
Reply-To: pierre@senellart.com, pgsql-bugs@lists.postgresql.org
Date: Sat, 18 Jul 2026 08:39:10 +0000
Message-ID: <19558-ad1fca59a3a471a0@postgresql.org>
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The following bug has been logged on the website:

Bug reference:      19558
Logged by:          Pierre Senellart
Email address:      pierre@senellart.com
PostgreSQL version: 19beta2
Operating system:   Linux
Description:       =20

The following works on PostgreSQL <=3D 18 but raises a syntax error on
19beta1/19beta2 (tested: PostgreSQL 19beta2, Ubuntu package
19~beta2-1.pgdg26.04+1, x86_64-linux):

    CREATE FUNCTION identity_int(int) RETURNS int
      LANGUAGE sql IMMUTABLE AS 'SELECT $1';
    CREATE OPERATOR |  (RIGHTARG =3D int, FUNCTION =3D identity_int);
    CREATE OPERATOR -> (RIGHTARG =3D int, FUNCTION =3D identity_int);

    SELECT | 5;    -- 18: returns 5;  19beta2: syntax error at or near "|"
    SELECT -> 5;   -- 18: returns 5;  19beta2: syntax error at or near "->"

Cause: the SQL/PGQ property graph patch turned "|" and "->" into dedicated
grammar tokens (RIGHT_ARROW), declared in the precedence list alongside Op.
Explicit binary productions (a_expr '|' a_expr, a_expr RIGHT_ARROW a_expr)
preserve infix use, and both tokens were added to the operator-name
productions, so binary use and the OPERATOR() syntax still work:

    SELECT OPERATOR(public.|) 5;    -- still returns 5 on 19beta2
    SELECT OPERATOR(public.->) 5;   -- still returns 5 on 19beta2

But no unary counterparts of these productions were added, so a user-defined
*prefix* operator spelled exactly "|" or "->" can no longer be invoked by
its bare name. Note the inconsistency: CREATE OPERATOR still accepts both
names for prefix operators; the resulting operator just cannot be called
except through OPERATOR().

If the tokenization is here to stay, could unary productions ('|' a_expr,
RIGHT_ARROW a_expr) be added to restore the pre-19 behaviour? Failing that,
this seems worth an entry in the release notes' incompatibilities section,
since nothing currently documents it.

Motivation: https://pgxn.org/dist/provsql/ which I am developing uses prefix
| as a probabilistic =E2=80=9Cgiven=E2=80=9D operator. This works on all Po=
stgreSQL versions
from 10 to 18, but fails on 19beta2.