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From: Tom Lane <tgl@sss.pgh.pa.us>
To: jiangshan.liu@tju.edu.cn
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18403: PL/pgSQL is reporting unexpected errors when
 processing DECLARE blocks with <<label>>
In-reply-to: <18403-7069fc75f5255783@postgresql.org>
References: <18403-7069fc75f5255783@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Wed, 20 Mar 2024 19:35:22 -0000"
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Date: Wed, 20 Mar 2024 17:02:06 -0400
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PG Bug reporting form <noreply@postgresql.org> writes:
> I have approximated the program to a clean situation. When I execute this
> program, the PL/pgSQL engine does not report errors to me:

> DO $$
> DECLARE
> DECLARE
>     var1 INT = 1;
> BEGIN
>     RAISE NOTICE '%', var1;
> END;
> $$;

That is not valid code according to the documentation, which clearly
says that every DECLARE must be followed by BEGIN and then END [1].
You happen to get away with it because of an undocumented "feature":
one of the options for a declaration statement is

                | K_DECLARE
                    {
                        /* We allow useless extra DECLAREs */
                    }

So the first DECLARE begins the block, and the second is an
ignored noise word.

> DO $$
> DECLARE
> <<label>>
> DECLARE
>     var1 INT = 1;
> BEGIN
>     RAISE NOTICE '%', var1;
> END;
> $$;

This, however, is flat wrong, and the error message seems
perfectly on-point to me:

> ERROR:  block label must be placed before DECLARE, not after
> LINE 3: <<label>>
>         ^

			regards, tom lane

[1] https://www.postgresql.org/docs/current/plpgsql-structure.html