i have this variable called order1 in the table called datetable and i want to display out the duplicate orders in sql. how do i do that? do i need to use group by ?

thanks in advance.! any help?

well i actually get the answers by doin this...
select order1 from datetable group by order1 having count(*) > 1

however now i want to compare the values date1 in the first duplicate orders to the second duplicate order...like compare aaaa of the first row and aaaa of the second row ...how to do that? i need to compare the date1 in minutes..i only wan duplicate orders with minutes difference less than 30mins

id Order1 date1
1 aaaaa 20051001 12:45
2 aaaaa 20051001 12:10
3 bbbbb 20031002 15:05
4 bbbbb 20031002 15:50