PostgreSQL: how to catch exception in a function? - postgresql

Question

I have a table and 3 functions
fntrans-calls->fntrans2-calls->fntrans3
In this example I have removed call of fntrans3();
After this call
SELECT public.fntrans2();
the table t2 contains records, ok, it is clear, rollback works to the savepoint inside of function
But when I do call
SELECT public.fntrans();
the table does not contain any rows and output shows notice about exception in fntrans;
Why in the 2nd case exception throwed to the 1st function but when I call fntrans2 only it caught inside this function.
create table t2(ID SERIAL PRIMARY KEY, f1 INTeger);
CREATE OR REPLACE FUNCTION "public"."fntrans" (
)
RETURNS integer AS
$body$
declare d double precision;
BEGIN
raise notice 'fntrans';
INSERT INTO t2 (f1) VALUES (1);
INSERT INTO t2 (f1) VALUES (2);
INSERT INTO t2 (f1) VALUES (3);
select fntrans2();
INSERT INTO t2 (f1) VALUES (4);
RETURN 1;
EXCEPTION
WHEN OTHERS THEN
BEGIN
raise notice 'fntrans exception';
RETURN 0;
END;
END;
$body$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER
COST 100;
CREATE OR REPLACE FUNCTION public.fntrans2 (
)
RETURNS integer AS
$body$
declare d double precision;
BEGIN
raise notice 'fntrans2';
INSERT INTO t2 (f1) VALUES (10);
INSERT INTO t2 (f1) VALUES (22);
INSERT INTO t2 (f1) VALUES (30);
BEGIN
raise exception 'Oooooppsss 2!';
INSERT INTO t2 (f1) VALUES (40);
RETURN 1;
EXCEPTION
WHEN OTHERS THEN RETURN 0;
END;
END;
$body$
LANGUAGE 'plpgsql' VOLATILE;
CREATE OR REPLACE FUNCTION public.fntrans3 (
)
RETURNS integer AS
$body$
declare d double precision;
BEGIN
raise notice 'fntrans3';
INSERT INTO t2 (f1) VALUES (100);
INSERT INTO t2 (f1) VALUES (200);
INSERT INTO t2 (f1) VALUES (300);
raise exception 'Oooooppsss 3!';
INSERT INTO t2 (f1) VALUES (400);
RETURN 1;
EXCEPTION
WHEN OTHERS THEN RETURN 0;
END;
$body$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER
COST 100;

Answer 1

Your problem is the line
select fntrans2();
in fntrans. You cannot use SELECT without an INTO clause in PL/pgSQL.
Without the EXCEPTION block you'll get the following message:
CONTEXT: SQL statement "select fntrans2()"
PL/pgSQL function fntrans() line 8 at SQL statement
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 fntrans() line 8 at SQL statement
That is pretty self-explanatory.
It also explains why you don't see any results from the function fntrans2 – it doesn't get called.
You could change the offending line to
PERFORM fntrans2();