How to calculate DATE Difference in PostgreSQL?

Here I need to calculate the difference of the two dates in the PostgreSQL.

In SQL Server: Like we do in SQL Server its much easier.

DATEDIFF(Day, MIN(joindate), MAX(joindate)) AS DateDifference; 

My Try: I am trying using the following script:

(Max(joindate) - Min(joindate)) as DateDifference; 

Question:

• Is my method correct?

• Is there any function in PostgreSQL to calculate this?

6 Answers

Your calculation is correct for DATE types, but if your values are timestamps, you should probably use EXTRACT (or DATE_PART) to be sure to get only the difference in full days;

EXTRACT(DAY FROM MAX(joindate)-MIN(joindate)) AS DateDifference 

An SQLfiddle to test with. Note the timestamp difference being 1 second less than 2 full days.

CAST both fields to datatype DATE and you can use a minus:

(CAST(MAX(joindate) AS date) - CAST(MIN(joindate) AS date)) as DateDifference 

Test case:

SELECT (CAST(MAX(joindate) AS date) - CAST(MIN(joindate) AS date)) as DateDifference FROM generate_series('2014-01-01'::timestamp, '2014-02-01'::timestamp, interval '1 hour') g(joindate); 

Result: 31

Or create a function datediff():

CREATE OR REPLACE FUNCTION datediff(timestamp, timestamp) RETURNS int LANGUAGE sql AS $$ SELECT CAST($1 AS date) - CAST($2 AS date) as DateDifference $$; 

a simple way would be to cast the dates into timestamps and take their difference and then extract the DAY part.

if you want real difference

select extract(day from 'DATE_A'::timestamp - 'DATE_B'::timestamp); 

if you want absolute difference

select abs(extract(day from 'DATE_A'::timestamp - 'DATE_B'::timestamp)); 

This is how I usually do it. A simple number of days perspective of B minus A.

DATE_PART('day', MAX(joindate) - MIN(joindate)) as date_diff 

This is not a direct answer to OP's question, however, this is the answer I was looking for when my search brought me to this thread.

For someone who wants to create a human-readable string that denotes the difference between two dates, consider using AGE().

 AGE(table.end_date, table.start_date) 

It produces results that looks like these:

0:00:27 3 days 22:06:39.833264 4 days 01:12:39.473559 20 days 17:53:20.23287 23 days 21:01:15.150703 1 mon 19 days 01:52:24.262275 2 mons 17 days 05:04:12.277099 2 mons 17 days 04:59:21.618069 

If you have a timestamp already you will need not to cast anything,

For the absolute difference @zubair-0 answer is great here is implementation an using...

select abs(extract(day from A - B)) from table_name; 

Note: A and B are timestamps as data types