Validation for Duplicate Record in Table Control

Hi All,

I have been developing a dialog program in which i used table control manually (WITHOUT WIZARD). now the table control first column is MATERIAL CODE and is a mandatory field,here i have to do two things.

1. I need to throw an error message when the material code already entered.i.e for eg. if the user enters this material code FDH01106DSAAAB0006 again, then i need to throw error message immediately .

2.After removing the material code, since it is a mandatory field, the screen is not getting enabled and it is giving message "Fill in all required entry fields".

  here i need to enable the screen.

Please guide me in resolving these issues.

Thanks in Advance.................!