custon table

Hi,

i have created a custom table in SE11

and now i want to populate it..when i got o SM30 and inputed a thesame value it will have an error:"An entry already exists with the same key".

Does anyone here knows how to populate the table with one field has the same value with the previous..

example i want to populate the table with:

A582 * A 1:00:00 2:00:00

A582 * L 3:00:00 4:00:00

A582 * N 6:00:00 9:00:00

i hope someone could help me...

thank you...

regards,

mae