stop duplication in one subform

[steve111]

hi

I have a form, and 3 subforms within it

the first form lets me select a "group no" and description
the first subform lets me select a assemble part number and is linked via that group number
the second subform lets me select parts for the assembly
the last subform let me allocate the contract number, date "BOM" was created

what I cannot have but has happened is that the user has selected the group twice, using 2 different assemble part numbers and parts for one contract . this is wrong

is it possible that when he enters the contract number in the 3rd subform
it can see it has been duplicated by looking at the group number in the main form of. the contract number could be assigned to many group numbers but not twice

thanks
steve

 

[Ranman256]

can you not key the table so a user CANT enter duplicates?