problem in table control

Hi experts,

I m having a table control as a selection screen.When I enter a material number in the first field of the table control and press enter, then i m doing some validations for some fields and populating the data into the fields of the table control by using the material no.This is working fine.After that again if i press enter,again the process is starting and data in the 1st row is copied to 2nd row.If i press enter again the process is repeating and the rows are filled with the same data of 1st row.How can i prevent this?any suggestions please?

Thanks,

dp.