Re: PL/pgSQL doesn't support variables in queries?

["J.A." <postgresql@xxxxxxxxxxxxxxxxxxxxxxx>]

Oh wow folks! I totally misunderstood the docs then. (I also tried to Read The Manual before I posted here, too :blush:)

I must admit, I did try doing something like you suggested Erik. I tried things like:

DO $$
        DECLARE
          v_application_id uuid;
        BEGIN
          SELECT application_id INTO v_application_id FROM applications WHERE code = 'pg-test-cc';
          

          SELECT * FROM application_foo WHERE application_id = v_application_id;
          -- more SELECT * FROM child tables....

        END $$;

but that never worked, with warning:

ERROR: query has no destination for result data HINT: If you want to discard the results of a SELECT, use PERFORM instead. CONTEXT: PL/pgSQL function inline_code_block line 7 at SQL statement SQL state: 42601

Which is why i (incorrectly?) thought this cannot be done?

So is there another trick to doing this instead? Is it maybe via the v_record "record" variable instead?

-JA-

On Wed, 3 May 2023 at 22:39, Erik Wienhold <ewie@xxxxxxxxx> wrote:

> On 03/05/2023 14:25 CEST J.A. <postgresql@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> ms-sql person here migrating over to pgsql. One of the first thing's I noticed
> with pgsql (or more specifically, PL/pgSQL) is that it doesn't support
> "variables" in a query?
>
> for example, here's some T-SQL:
>
> DECLARE @fkId INTEGER
>
> SELECT @fkId = fkId FROM SomeTable WHERE id = 1
>
> -- and then do something with that value..
>
> SELECT * FROM AnotherTable WHERE Id = @fkId
> SELECT * FROM YetAnotherTable WHERE FKId = @fkId
> -- etc..

plpgsql does support variable declarations [0] but does not use any special
notation like T-SQL.  An equivalent to your example would be:

        DO $$
        DECLARE
          v_fkid int;
          v_rec record;
        BEGIN
          SELECT fkid INTO v_fkid FROM SomeTable WHERE id = 1;
          SELECT * INTO v_rec FROM AnotherTable WHERE Id = v_fkid;
          -- Do something with v_rec ...
        END $$;

Prefixing variable names with v_ is just a convention to avoid ambiguous column
references (assuming that column names are not prefixed with v_) [1].

[0] https://www.postgresql.org/docs/current/plpgsql-declarations.html
[1] https://www.postgresql.org/docs/current/plpgsql-implementation.html#PLPGSQL-VAR-SUBST

--
Erik