Count months between two timestamp on postgresql?

Question

I want to count the number of months between two dates.

Doing :

SELECT TIMESTAMP \'2012-06-13 10:38:40\' - TIMESTAMP \'2011-04-30 14:38:40\';
         


        

Answer 1

Please note that the most voted answer by @ram and @angelin is not accurate when you are trying to get calendar month difference using.

select extract(year from age(timestamp1, timestamp2))*12 + extract(month from age(timestamp1, timestamp2))

for example, if you try to do:

select extract(year from age('2018-02-02'::date, '2018-03-01'::date))*12 + extract(month from age('2018-02-02'::date , '2018-03-01'::date))

the result will be 0 but in terms of months between March from February should be 1 no matter the days between dates.

so the formula should be like the following saying that we start with timestamp1 and timestamp2:

((year2 - year1)*12) - month1 + month2 = calendar months between two timestamps

in pg that would be translated to:

select ((extract('years' from '2018-03-01 00:00:00'::timestamp)::int -  extract('years' from '2018-02-02 00:00:00'::timestamp)::int) * 12) 
    - extract('month' from '2018-02-02 00:00:00'::timestamp)::int + extract('month' from '2018-03-01 00:00:00'::timestamp)::int;

you can create a function like:

CREATE FUNCTION months_between (t_start timestamp, t_end timestamp)
RETURNS integer
AS $$
select ((extract('years' from $2)::int -  extract('years' from $1)::int) * 12) 
    - extract('month' from $1)::int + extract('month' from $2)::int
$$
LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;