Unique key with NULLs

Question

This question requires some hypothetical background. Let\'s consider an employee table that has columns name, date_of_birth, tit

Answer 1

Your problem of not having duplicates based on name is not solvable because you do not have a natural key. Putting a fake date in for people whose date of birth is unknown will not solve your problem. John Smith born 1900/01/01 is still going to be a differnt person than John Smithh born 1960/03/09.

I work with name data from large and small organizations every day and I can assure you they have two different people with the same name all the time. Sometimes with the same job title. Birthdate is no guarantee of uniqueness either, plenty of John Smiths born on the same date. Heck when we work with physicians office data we have often have two doctors with the same name, address and phone number (father and son combinations)

Your best bet is to have an employee ID if you are inserting employee data to identify each employee uniquely. Then check for the uniquename in the user interface and if there are one or more matches, ask the user if he meant them and if he says no, insert the record. Then build a deupping process to fix problems if someone gets assigned two ids by accident.