postgresql error : Multiple decimal points - postgresql

Question

So I'm having this query:
SELECT
TO_CHAR(date_part('hour', created_at), 'YYYY-MM-DD HH24'),
to_char(created_at, 'day') ",
COUNT(*) AS "
FROM table
GROUP BY 1,2
ORDER BY 1 DESC
When I execute the query I get this:
ERROR: multiple decimal points
Searching stackoverflow I found some recommendations here:
How to format bigint field into a date in Postgresql? but I don't get why do I have to divide by 1000 and how this would apply in the case of the date_part function.

Answer 1

I assume created_at is a timestamp?.. I'm choosing from date_part(text, timestamp) and date_part(text, interval), if so date_part will return a double precision, to which you try to apply the mask 'YYYY-MM-DD HH24', eg:
v=# select date_part('hour', now());
date_part
-----------
9
and I don't see how you could possibly get year, month, day and hour from nine...
Yet I assume you wanted to apply the mask against truncated date to the hour precision, which is done with date_trunc(text, timestamp):
v=# select date_trunc('hour', now());
date_trunc
------------------------
2017-06-20 09:00:00+01
(1 row)
so now you can apply the time format:
v=# select to_char(date_trunc('hour', now()),'YYYY-MM-DD HH24');
to_char
---------------
2017-06-20 09
(1 row)
but if this is what you want, then you don't need to truncate time at all:
v=# select to_char(now(),'YYYY-MM-DD HH24');
to_char
---------------
2017-06-20 09
(1 row)
https://www.postgresql.org/docs/current/static/functions-datetime.html