Using variables in PostgreSQL function - function

Question

I get this error when I try to run a custom PostgreSQL function:
ERROR: query has no destination for result data
PostgreSQL functions are very new for me. I am working with Navicat for PostgreSQL 11.0.17.
I have a table named translations with three columns: id, english, français. Here is how I create my function in the Console window:
test=# CREATE FUNCTION add_translation(english varchar(160), français varchar(160))
RETURNS integer
AS $BODY$
DECLARE
translation_id integer;
BEGIN
INSERT INTO translations
("english", "français")
VALUES (english, français)
RETURNING id
AS translation_id;
RETURN translation_id;
END;
$BODY$
LANGUAGE plpgsql;
Query OK, 0 rows affected (0.02 sec)
When I call this from the Console window, I get a not-very-useful error message.
test=# add_translation('one', 'un');
ERROR: syntax error at or near "add_translation"
LINE 1: add_translation('one', 'un')
^
When I call it from the Design Function window, I get the error quoted at the top.
I specifically want to isolate translation_id, because in the final version of this function I want to insert the latest id from the translation table into a new record in a different table.
I have also tried with:
DECLARE
translation_id integer;
BEGIN
INSERT INTO translations
("english", "français")
VALUES (english, français);
SELECT LASTVAL() INTO translation_id;
RETURN translation_id;
END;
When I run this from the Design Function panel, it behaves correctly, but when I call it from the console I get the same error as before.
If you can recommend any good tutorials and examples for understanding how to use variables correctly in postgres functions, I would be most grateful.

Answer 1

From the console you need a select command
select add_translation('one', 'un');
or
select * from add_translation('one', 'un');
Your function can be plain SQL
create or replace function add_translation (
english varchar(160), français varchar(160)
) returns integer as $body$
insert into translations ("english", "français")
values (english, français)
returning id as translation_id;
$body$ language sql;
In plpgsql a setof some type must be "returned from" the query
create or replace function add_translation (
english varchar(160), français varchar(160)
) returns setof integer as $body$
begin
return query
insert into translations ("english", "français")
values (english, français)
returning id as translation_id;
end;
$body$ language plpgsql;
Or to return a single value do the insert inside a CTE
create or replace function add_translation (
english varchar(160), français varchar(160)
) returns integer as $body$
declare
translation_id integer;
begin
with i as (
insert into translations ("english", "français")
values (english, français)
returning id
)
select id into translation_id from i;
return translation_id;
end;
$body$ language plpgsql;