MySQL-用第二行的第二列减去第一行的第一列

Question

I'm struggling with a Mysql Code, and I have no clue how to solve this. I have two columns with time value on which I've ordered by desc in Mysql Query result.

I need to find out the differences between the 2nd row StateEndTime and the 1st-row StateStarTtime nd so on and display this in a new row/column. The final table should look like this :

ID          Type         StateStarTtime    StateEndTime   Min Difference

xxx         YYY          03:57             03:59          00:02
xxx         ZZZ          03:53             03:55          00:04
xxx         ZZZ          03:46             03:49          

Answer 1

SELECT id,startTime,endTime,type,TIMEDIFF(endTime,startTime) as min_df FROM tasks where 1

Answer 2

You must get the max(stateendtime) that is less than the current row's stateendtime
and subtract it from statestarttime :

select 
  t.*,
  left(timediff(
   t.statestarttime, 
   select max(stateendtime) from tablename where stateendtime < t.stateendtime
  ), 5) mindifference
from tablename t
order by t.statestarttime desc