PostgreSQL & division_by_zero exception - postgresql

Question

I can't quite get this right.. my function looks like:
create or replace function myfunc(integer, varchar(25), varchar(25), integer, integer) returns numeric as $$
declare var_return numeric;
begin
select sum(a+ b) / sum(a + b + c)
from mytable
where col1 = $1
and col2 = $2
and col3 = $3
and col4 between $4 AND $5
into var_return;
exception when division_by_zero then return 0.0;
return coalesce(var_return, 0.0);
end;
$$ language plpgsql;
But when I do select myfunc(123, 'foo', 'bar', 1, 10); I see:
ERROR: control reached end of function without RETURN
CONTEXT: PL/pgSQL function "myfunc"
Why does this happen? Clearly I want to catch when the select statement encounters a case where a + b + c equals 0 and return 0.

Answer 1

The EXCEPTION clause pertains to the entire BEGIN block, and runs until the END. That is, Postgres understands you to have written this:
create or replace function myfunc(...) returns ... as $$
declare var_return numeric;
begin
select ...
into var_return; -- but no RETURN statement in this block
exception when division_by_zero then
return 0.0;
return coalesce(var_return, 0.0); -- this is part of the exception handler
end;
$$ language plpgsql;
Move your "RETURN COALESCE..." above the EXCEPTION line, and try again.

Answer 2

You can vastly simplify your function:
CREATE OR REPLACE FUNCTION myfunc(int, varchar(25), varchar(25), int, int)
RETURNS numeric AS
$BODY$
SELECT CASE WHEN abc = 0 THEN 0::numeric ELSE (ab/abc)::numeric END
FROM (
SELECT sum(a + b) AS ab, sum(a + b + c) AS abc
FROM mytable
WHERE col1 = $1
AND col2 = $2
AND col3 = $3
AND col4 BETWEEN $4 AND $5
) x;
$BODY$ language SQL;
Major points
This is language SQL, not a PL/pgSQL function. You can use either, but for a simple case like this you might as well stick with the simpler tool.
#pilcrow diagnosed the cause of your error accurately. The way you have it, the RETURN statement is part of the exception handler and is only ever reached if an exception occurs.
If the data type of a, b, c should be integer or bigint, you probably want to cast to numeric before the division or the results will be coerced to integers.
Use a CASE statement to avoid division by zero. This is much cheaper than exception handling.

Answer 3

Are you sure that you handle the right exception ?
I guess that you have another exception.
See a list of exception you can trap.
I would try first ( I always put exceptions at the end of the block, easier to read.)
create or replace function myfunc(integer, varchar(25), varchar(25), integer, integer) returns numeric as $$
declare var_return numeric;
begin
select sum(a+ b) / sum(a + b + c)
from mytable
where col1 = $1
and col2 = $2
and col3 = $3
and col4 between $4 AND $5
into var_return;
return coalesce(var_return, 0.0);
exception
when division_by_zero then
return 0.0;
when others then
RAISE NOTICE 'caught others';
return 0.0;
end;
$$ language plpgsql;