I'm creating database to keep track of documentation. For this database i have tblStudy, tblSite and tblDoc. Based on the tblStudy and tblDoc i created frmMain. On the top of the form user select from the combo box if the documentation is for "Reg" or "Site".

when user select from combo box "Reg" combo box "cboStudy" becomes visible where they can select the Study.

when user select from combo box "Site" combo box "cboSite" becomes visible where user will first select the Site and then "cboStudy" will be visible where user can select Study for that site.

This is the problem i have :

Lets say for first record user select "Reg" from comb box and then enter StudyNo:123 with all other corresponding information.

Now for the secound record user select "Site" from combo box which will allow user to select the site first and lets say user selects SiteNo: 100 and then user will add new Study for the SiteNo 100 and what if user enters StudyNo 123 for that site ?

StudyNo is PK so is there anyother way to handle this situation. I can remove PK from StudyNo but then it would create lot of duplicate value.

Thanks In Advance