When i use below sql command
==>
select (DC.p_date - ( select min(DC.p_date) from DC) )*48 as interval from DC
Note: DC.p_date - ( select min(DC.p_date) from DC) )*48 --> to get the ineterval erery 30 min.
result is like below :
interval
------------------
94 08:44:0
332 19:26:2
332 19:26:2
333 02:39:1
but i should use what kind of sql function to change '94 08:44:0' to a double or integer (use trunc will fair)