Question

I have a query that I have simplified and written below.
How do I display the time difference of 2 fields that were calculated as 2 separate inline select statements?

SELECT x.name ,
   ( SELECT data.ts 
     FROM data 
     WHERE prim_key = x.prim_key and roll_no ='1'  
 ) **starttime** ,
  ( SELECT data.ts 
    FROM woman_data 
    WHERE prim_key = x.prim_key and roll_no ='10'

) **endtime**
, **TIME_TO_SEC( TIMEDIFF( endtime , starttime)** as timediff // This line does not work.It cannot recognize endtime ans starttime
FROM data x 
     INNER JOIN  y 
ON x.prim_key = y.prim_key
ORDER BY x.prim_key

Answer 1

try this:

starttime and endtime are derived columns, you cannot use it in the same select statement..
You have to create a derived table then use these columns the a query outside

select name,starttime,endtime,TIME_TO_SEC( TIMEDIFF( endtime , starttime) as timediff
from(
SELECT x.name ,
   ( SELECT data.ts 
     FROM data 
     WHERE prim_key = x.prim_key and roll_no ='1'  
 ) starttime ,
  ( SELECT data.ts 
    FROM woman_data 
    WHERE prim_key = x.prim_key and roll_no ='10'

) endtime

FROM data x 
     INNER JOIN  y 
ON x.prim_key = y.prim_key)a
ORDER BY x.prim_key