如何在MySQL中计算当前行与上一行之间的时差

Question

I have mysql table t1 like this :

What i want to do is do calculations between all rows and save the value in new coloumn called diff

TICKETID| DATENEW  | DIFF
16743     12:36:46   0
16744     12:51:25   15.  minute  
16745     12:57:25   6.5  minute
..........
.......
etc

i know there are similar questions ,but ive tried all of the solutions posted here with no success,so how to solve this query ???

Answer 1

To get the time difference in minutes between the current and previous row, you can use timestampdiff on datenow and the previous time, which you can get via subquery:

select ticketid, datenew,
    timestampdiff(minute,datenew,(select datenew from mytable t2
        where t2.ticketid < t1.ticketid order by t2.ticketid desc limit 1)) as diff
from mytable t1

Update

Here's another way using a variable to store the previous datenew value that might be faster:

select ticketid, datenew, timestampdiff(minute,datenew,prevdatenew)
from (
    select ticketid, datenew, @prevDateNew as prevdatenew, 
      @prevDateNew := datenew
    from mytable order by ticketid
) t1

Answer 2

select 
 t1.*
,coalesce(timestampdiff(MINUTE,t2.dt,t1.dt),0) as tdiff 
from t t1 left join t t2
on t1.id = t2.id+1
order by t1.id

As you are only looking for a difference between the current row and the next, you can join on the next row and calculate the time difference in minutes.

Note: This assumes there are no missing id's in the table. You might have to change the join condition if there were missing id's.

SQL Fiddle: http://www.sqlfiddle.com/#!9/4dcae/15