42702 'column reference “id” is ambiguous' for RETURNING of table-returning PL/pgSQL function
-
03-03-2021 - |
Question
This works:
CREATE OR REPLACE FUNCTION sql_fun()
RETURNS TABLE (id UUID) AS $$
INSERT INTO foo DEFAULT VALUES
RETURNING id
$$ LANGUAGE SQL;
SELECT *
FROM sql_fun();
This doesn't:
CREATE OR REPLACE FUNCTION plpgsql_fun()
RETURNS TABLE (id UUID) AS $$
BEGIN
RETURN QUERY
INSERT INTO foo DEFAULT VALUES
RETURNING id;
END
$$ LANGUAGE PLpgSQL;
SELECT *
FROM plpgsql_fun();
Is this a bug in PL/pgSQL? How can I fix this while keeping the return type as is?
Solution
The solution is to qualify all columns from RETURNING
which have the same name as the columns from RETURNS TABLE
with the name of the table which was INSERTED INTO
:
CREATE OR REPLACE FUNCTION plpgsql_fun()
RETURNS TABLE (id UUID) AS $$
BEGIN
RETURN QUERY
INSERT INTO foo DEFAULT VALUES
RETURNING foo.id;
END
$$ LANGUAGE PLpgSQL;
If the name of the table is long and there are multiple columns, the name can be aliased:
CREATE OR REPLACE FUNCTION plpgsql_fun()
RETURNS TABLE (id UUID, foo INT, bar INT) AS $$
BEGIN
RETURN QUERY
INSERT INTO table_with_a_very_long_name AS x DEFAULT VALUES
RETURNING x.id, x.foo, x.bar;
END
$$ LANGUAGE PLpgSQL;
OTHER TIPS
How can I fix this while keeping the return type as is?
You can even fix it keeping the whole function as is, by adding the special configuration parameter #variable_conflict
:
CREATE OR REPLACE FUNCTION plpgsql_fun()
RETURNS TABLE (id UUID) AS $$
#variable_conflict use_column
BEGIN
RETURN QUERY
INSERT INTO foo DEFAULT VALUES
RETURNING id;
END
$$ LANGUAGE plpgsql; -- see below
But it's good form to do it by table-qualifying columns names, like you found yourself - if at all possible. There are corner cases, where it's not easily possible:
Related:
- INSERT INTO … RETURNING - ambiguous column reference
- How to return result of a SELECT inside a function in PostgreSQL?
In early versions, Postgres did not raise an exception, but silently preferred parameter values over columns:
And avoid CaMeL-casing the language name plpgsql
. That stops working when quoted, which (unfortunately) is a wide-spread malpractice.