In PostgreSQL, the justify_days() function allows you to adjust an interval value, so that 30-day time periods are represented as months.

For example, if you have an interval of say, 30 days, justify_days() will return it as 1 mon.

Syntax

The function has the following syntax:

justify_days(interval)

Where interval is the interval that you want represented in months.

Example

Here’s a basic example to demonstrate.

SELECT justify_days(interval '30 days');

Result:

1 mon

Partial Months

Here’s an example of what happens when your interval isn’t an exact multiple of 30 days.

\x
SELECT 
  justify_days(interval '31 days'),
  justify_days(interval '45 days'),
  justify_days(interval '290 days');

Result (using vertical output):

justify_days | 1 mon 1 day
justify_days | 1 mon 15 days
justify_days | 9 mons 20 days

In this example I used \x to switch over to expanded display, which displays the results using vertical output. This makes it slightly easier to read the results.

Less than a Month

If the interval is less than 30 days, then it will remain in days.

SELECT justify_days(interval '29 days');

Result (using vertical output):

29 days

Including Minutes

In this example, the interval includes a minutes part.

SELECT justify_days(interval '40 days 30 minutes');

Result (using vertical output):

1 mon 10 days 00:30:00

So in this case we end up with a time value being appended to the result.