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From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Date: Fri, 10 Apr 2026 21:55:00 +0530
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 <CAExHW5s5Q4U3GPHaGJMAZBb8=7bm4pDc9_MWi5AsTaFC-OB2HQ@mail.gmail.com>
Subject: Re: Bug: Missing collation assignment for GRAPH_TABLE COLUMNS
 expressions
To: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Peter Eisentraut <peter@eisentraut.org>
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Hi Satya,
Thanks for the report and patch.

On Fri, Apr 10, 2026 at 9:12=E2=80=AFPM SATYANARAYANA NARLAPURAM
<satyanarlapuram@gmail.com> wrote:
>
> Hi hackers,
>
> GRAPH_TABLE COLUMNS expressions that involve collation-dependent function=
s or operators fail with:
>
>   ERROR: could not determine which collation to use for upper() function
>   HINT: Use the COLLATE clause to set the collation explicitly.
>
> Setup:
>
>   CREATE TABLE vtx (id int PRIMARY KEY, name text);
>   CREATE TABLE edg (id int PRIMARY KEY,
>                     src int REFERENCES vtx(id),
>                     dst int REFERENCES vtx(id));
>   INSERT INTO vtx VALUES (1,'Alice'),(2,'Bob'),(3,'Carol');
>   INSERT INTO edg VALUES (1,1,2),(2,2,3);
>
>   CREATE PROPERTY GRAPH g
>     VERTEX TABLES (vtx KEY (id))
>     EDGE TABLES (edg KEY (id)
>       SOURCE KEY (src) REFERENCES vtx (id)
>       DESTINATION KEY (dst) REFERENCES vtx (id));
>
> postgres=3D# SELECT * FROM GRAPH_TABLE (g
>   MATCH (a IS vtx)-[e IS edg]->(b IS vtx) COLUMNS (upper(a.name) AS src_u=
pper));
> ERROR:  could not determine which collation to use for upper() function
> HINT:  Use the COLLATE clause to set the collation explicitly.
>
>
> In transformRangeGraphTable(), the COLUMNS transformation loop calls tran=
sformExpr()
> on each column expression but omits the subsequent assign_expr_collations=
() call.  Both
> WHERE clause transformation sites in parse_graphtable.c correctly include=
 it.
>
> Attached a patch to fix this.

I think the fix is in the right direction. It's better to call
assign_expr_collation only once on all the columns at the end of loop
of rgt->columns, just like assign_expr_collation is called on all the
conditions in WHERE clause once.

Good to see tests also included in the patch. Do we need all three
queries? Also those queries should be placed near the section "-- test
collation specified in the expression" and add a query for explicit
collation in COLUMNs expression.

--=20
Best Wishes,
Ashutosh Bapat