I have a Tbl_Strucutre with 4 combo fields. I need the records to be unique, however, all 4 fields do not need to be completed. I can't set the primary key to all 4 fields because some fields can be blank. For example, the following entries would be valid.
Column1 Column2 Column3 Column4
cat hat sat fat
cat hat sat
cat run sun
dog blog hog fog
How do I keep the user from entering duplicate records in a form while including blanks?