How to store Derived Column in MySQL

Question

I have a table A which have Start_time and End_time as columns, i am calculating the difference of these two columns as

Select timediff(End_time, Start_time) as TF from A

Now i want to sum of all time periods present ln TF column.

I searched alot but could not found anything related to it

Answer 1

Timediff() will give you result in HH:MM:SS format. In order to SUM() them up, you need to first convert them into numbers (in this case, seconds); add them up using SUM() ; and then convert them back to HH:MM:SS format:

SELECT SEC_TO_TIME( SUM( TIME_TO_SEC( TIMEDIFF(End_time, Start_time) ) ) ) 
FROM A