last_day in PostgreSQL

问题

The oracle last_day function return the last day of the month. example:

nls_date_format='YYYY-MM-DD H24:MI:SS'
select last_day(sysdate) from dual;
LAST_DAY(SYSDATE)
-------------------
2014-06-30 15:45:43

oracle return the time value as well.

I have tried below sql in PostgreSQL which return the last day of month but time value is "00:00:00".

select (date_trunc('month', now()) + interval '1 month -1 day')::timestamp(0);
         ?column?          
---------------------------
 2014-06-30 00:00:00
(1 row)

the sql return the date correctly but I want date and time like oracle.

回答1:

select (
    date_trunc('month', now())
    + interval '1 month -1 day'
    + now()::time
)::timestamp(0);

回答2:

The function last_day() should do the trick. This function should be found in a extenstion package called "orafce". Containing other functions used in Oracle.

1. Install the correct version of orafce package (if needed):

   apt-get install postgresql-9.1-orafce
   

2. SQL:

   Create Extension orafce
   

3. If error rename orafce--3.0.sql to orafce--3.03.sql or user later version of orafce.

4. Use the function:

   SELECT last_day('2015-01-01')
   

Works like expected and the result is '2015-01-31'

来源：https://stackoverflow.com/questions/24307073/last-day-in-postgresql