PL/pgSQL anonymous code block

Question

In PostgreSQL 9.0 I have this PLPGSQL anonymous code block:

DO $$
    DECLARE
        bigobject integer;
    BEGIN
        SELECT lo_creat(-1) INTO bigobject         


        

Answer 1

This is an artifact of the fact that PostgreSQL has two completely different kinds of SQL statements internally - plannable (SELECT, INSERT, UPDATE, and DELETE) and unplannable (everything else) statements.

Only plannable statements support query parameters.

PL/pgSQL implements variable substitutions into statements, like your bigobject, using query parameters.

Because they aren't supported for non-plannable statements, no substitution is performed. So PL/pgSQL tries to execute the statement literally, as if you'd typed:

ALTER LARGE OBJECT bigobject OWNER TO postgres;

directly at the psql prompt. It does not detect this as an error.

To work around this, use EXECUTE ... FORMAT, e.g.

EXECUTE format('ALTER LARGE OBJECT %s OWNER TO postgres', bigobject);

See this related answer about COPY.