How to get the last day of month in postgres? - sql

Question

How to find the last day os the month in postgres?
I have a date columns stored as numeric(18) in the format(YYYYMMDD)
I am trying it to make it date using
to_date("act_dt",'YYYYMMDD') AS "act date"
then find the last day of this date:
like this:
(select (date_trunc('MONTH',to_date("act_dt",'YYYYMMDD')) + INTERVAL '1 MONTH - 1 day')::date)
but it gives me this error:
ERROR: Interval values with month or year parts are not supported
Detail:
-----------------------------------------------
error: Interval values with month or year parts are not supported
code: 8001
context: interval months: "1"
query: 673376
location: cg_constmanager.cpp:145
process: padbmaster [pid=20937]
-----------------------------------------------
Any help?
Postgres version:
PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3), Redshift 1.0.874

Answer 1

For anybody coming to this question looking for the Postgres way to do this (not using Redshift), here's how you'd do it:
SELECT (date_trunc('month', '2017-01-05'::date) + interval '1 month' - interval '1 day')::date
AS end_of_month;
Replacing the '2017-01-05' with whatever date you want to use. You can make this into a function like this:
create function end_of_month(date)
returns date as
$$
select (date_trunc('month', $1) + interval '1 month' - interval '1 day')::date;
$$ language 'sql'
immutable strict;
EDIT Postgres 11+
Pulling this out of the comments from #Gabriel, you can now combine interval expressions in one interval (which makes things a little shorter):
select (date_trunc('month', now()) + interval '1 month - 1 day')::date as end_of_month;
-- +--------------+
-- | end_of_month |
-- +--------------+
-- | 2021-11-30 |
-- +--------------+
-- (1 row)

Answer 2

If you're using Amazon AWS Redshift then you can use Redshift's LAST_DAY function. While Redshift is based on PostgreSQL, the LAST_DAY function is not available in PostgreSQL, for a solution for PostgreSQL see #wspurgin's answer.
https://docs.aws.amazon.com/redshift/latest/dg/r_LAST_DAY.html
LAST_DAY( { date | timestamp } )
LAST_DAY returns the date of the last day of the month that contains date. The return type is always DATE, regardless of the data type of the date argument.
For example:
SELECT LAST_DAY( TO_DATE( act_date, 'YYYYMMDD' ) )

Answer 3

Okay, so you've got a numeric(18) column containing numbers like 20150118. You can convert that to a date like:
to_date(your_date_column::text, 'YYYYMMDD')
From a date, you can grab the last day of the month like:
(date_trunc('month', your_date_column) +
interval '1 month' - interval '1 day')::date;
Combined, you'd get:
select (date_trunc('month', to_date(act_dt::text, 'YYYYMMDD')) +
interval '1 month' - interval '1 day')::date
from YourTable;
Example at SQL Fiddle.

Answer 4

date_trunc('month',current_date) + interval '1 month' - interval '1 day'
Truncating any date or timestamp to the month level will give you the first of the month containing that date. Adding a month gives you the first of the following month. Then, removing a day will give you the date of the last day of the month of the provided date.

Answer 5

For future searches, Redshift does not accept INTERVAL '1 month'. Instead use dateadd(month, 1, date) as documented here.
To get the end of the month use: DATEADD(DAY, -1, (DATE_TRUNC('month', DATEADD(MONTH, 1, date))))

Answer 6

select to_char(date_trunc('month', now() + '01 Months'::interval) - '01 Days'::interval, 'YYYYmmDD'::text)::numeric as end_period_n