How can I make an average of dates in MySQL? - sql

Question

How can I make an average between dates in MySQL?
I am more interested in the time values, hours and minutes.
On a table with:
| date_one | datetime |
| date_two | datetime |
Doing a query like:
SELECT AVG(date_one-date_two) FROM some_table WHERE some-restriction-applies;
Edit:
The AVG(date1-date2) works but I have no clue what data it is returning.

Answer 1

This seems a bit hackish, but will work for dates beteen ~ 1970 and 2030 (on 32 bit arch). You are essentially converting the datetime values to integer, averaging them, and converting the average back to a datetime value.
SELECT
from_unixtime(
avg(
unix_timestamp(date_one)-unix_timestamp(date_two)
)
)
FROM
some_table
WHERE
some-restriction-applies
There is likely a better solution out there, but this will get you by in a pinch.

Answer 2

select avg(datediff(date1,date2))
select avg(timediff(datetime,datetime))

Answer 3

SELECT date_one + (date_two - date_one) / 2 AS average_date
FROM thetable
WHERE whatever
You can't sum dates, but you can subtract them and get a time interval that you can halve and add back to the first date.

Answer 4

SELECT TIMESTAMPADD(MINUTE, TIMESTAMPDIFF(MINUTE, '2011-02-12 10:00:00', '2011-02-12 12:00:00')/2, '2011-02-12 10:00:00')
The result is
'2011-02-12 11:00:00'

Answer 5

CREATE TABLE `some_table`
(
`some_table_key` INT(11) NOT NULL AUTO_INCREMENT,
`group_name` VARCHAR(128) NOT NULL,
`start` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
`finish` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`some_table_key`)
);
SELECT
group_name,
COUNT(*) AS entries,
SEC_TO_TIME( AVG( TIME_TO_SEC( TIMEDIFF(finish, start) ) ) ) AS average_time
FROM some_table
GROUP BY
some_table.group_name
;
You should always specify the group you want when using group functions, you can end up in some nasty messes with the group functions if you later extend queries with JOIN etc and assume MySql will choose the right group for you.

Answer 6

thinking outloud you could do a datediff in minutes from a set time, average that and then add those minutes back to the set time...

Answer 7

AVG is a grouping function, which means it will sum all the rows in the table and divide by the row count. But it sounds like you want the average of two different columns, reported individually for each row. In that case, you should just compute it yourself: (date1+date2)/2. (MySQL may want some extra syntax to add those columns properly.)
The code you've written will give you the table's average elapsed time between date1 and date2.