On 4/13/16 1:36 PM, Daniel Lenski wrote:
Hi all,
Is there a good reason why the SIGN() function does not work with the
INTERVAL type? (It is only defined for numeric types.)
(http://www.postgresql.org/docs/9.5/static/functions-math.html)
The only thing that comes to mind is you can get some strange
circumstances with intervals, like '-1 mons +4 days'. I don't think that
precludes sign() though.
What I have come up with is this rather inelegant and error-prone case
statement:
How is it error prone?
case when x is null then null x>interval '0' then +1 when x<interval
'0' then -1 when x=interval '0' then 0 end
You don't need to handle null explicitly. You could do
SELECT CASE WHEN x > interval '0' THEN 1 WHEN x < interval '0' THEN -1
WHEN x = interval '0' THEN 0 END
Or, you could do...
CREATE FUNCTION sign(interval) RETURNS int LANGUAGE sql STRICT IMMUTABLE
AS $$
SELECT CASE WHEN $1 > interval '0' THEN 1 WHEN x < interval '0' THEN -1
ELSE 0 END
$$;
That works because a STRICT function won't even be called if any of it's
inputs are NULL.
Is there a more obvious way to do sign(interval)? Would it be
technically difficult to make it "just work"?
Actually, after looking at the code for interval_lt, all that needs to
happen to add this support is to expose interval_cmp_internal() as a
strict function. It already does exactly what you want.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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