hi everyone

i'm trying to do some work on finding the sum of the differences between 2 datetime fields in an Oracle (Oracle8) database

this below obviously doesn't work:
Code:
SELECT
 SUM(to_char(time_end,'YYYYMMDDHH24MI') - to_char(time_start,'YYYYMMDDHH24MI'))
FROM
 mydb.mytbl
WHERE
 vin=27723
i need to find the difference in hours between the time_start and time_end fields in each row, and then sum up the total of the differences for all the rows

Thanks!