Re: Unexpected behaviour of numeric datatype when mixed with,float4,

Tom Lane wrote:

>Ezequiel Tolnay <mail(at)etolnay(dot)com(dot)ar> writes:
>
>
>>CREATE DOMAIN currency AS numeric(15,4);
>>CREATE TABLE test (id serial, amt currency);
>>CREATE FUNCTION f_test(currency) RETURNS currency AS $$
>>DECLARE n currency;
>>BEGIN n := $1 * 0.2::float4;
>> INSERT INTO test (amt) VALUES (n); RETURN n;
>>END $$ LANGUAGE PLPGSQL;
>>
>>
>
>plpgsql doesn't currently enforce domain constraints, so the assignment
>to n isn't doing the rounding that you expect. Until someone gets
>around to fixing that, an explicit coercion is probably what you need:
>
> n := cast($1 * 0.2::float4 AS currency);
>
>
>
Please note that the critical issue is a column defined as numeric(15,4)
(through the domain alias), but still capable of containing numbers with
higher precision. I wonder how is it possible to store a numeric with
higher precision on a column where the precision is clearly defined. Are
the numeric values stored on a column always variable precision, and the
precision being only enforced on assignment? Wouldn't this impact
heavily in performance and disk space usage?
In any case, it looks like the only flaw is when inserting or updating
with a plpgsql variable into a column defined as a domain for a fixed
precision numeric.