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

There is a another way to do it. Adding a column(non-nullable) to represent the String value of date_of_birth column. The new column value would be ""(empty string) if date_of_birth is null.

We name the column as date_of_birth_str and create a unique constraint employee(name, date_of_birth_str). So when two recoreds come with the same name and null date_of_birth value, the unique constraint still works.

But the efforts of maintenance for the two same-meaning columns, and, the performance harm of new column, should be considered carefully.