How to get the difference between two timestamps in a readable format in PostgreSQL

I have a table in PostgreSQL with two columns, created_on and closed_on, which contain timestamps in Unix milliseconds. I want to get the difference between these two timestamps in a readable format, such as "1 year, 9 days, 1 hour, 6 minutes, 1 second".

My initial table :

I have tried the following query:

SELECT 
    (closed_on - created_on) * interval '1 millisecond' as interval1,
    justify_interval(32317561561 * interval '1 millisecond') as interval2,
    to_timestamp(closed_on / 1000)::timestamp - to_timestamp(created_on / 1000)::timestamp as interval3,
    to_timestamp(created_on / 1000)::timestamp as created_on,
    to_timestamp(closed_on / 1000)::timestamp as closed_on
FROM test

This query returns the following results:

However, the results are not as expected:

• interval1 only shows the hours, not the days, months, etc.
• interval2 incorrectly shows 14 days, when there should be 9 days in a year.
• interval3 shows the correct number of days, but it does not show the
  years or months.

Expected result:

1 year, 9 days, 1 hour, 6 minutes, 1 second

Fiddle : https://www.db-fiddle.com/f/xnXPVmtBEBDih83ZutBMZ4/0

>Solution :

According to https://www.postgresql.org/docs/current/functions-datetime.html, justify_interval counts with 30-day months and timestamp subtraction counts with 24-hour days. Without a calendar and concrete start/end timestamps, that’s the best you can do.

It seems you are looking for the age function instead:

age ( timestamp, timestamp ) → interval

Subtract arguments, producing a “symbolic” result that uses years and
months, rather than just days

SELECT age(to_timestamp(closed_on / 1000), to_timestamp(created_on / 1000))
FROM test

^{(online demo)}