How to create UNIQUE key in mysql with BLANK value?

Question

I have a mysql table users .

A column named Email contains NULL value.

I'm not able to create a unique key on email . It is showing an error saying duplicate value '' .

Answer 1

That's because you have multiple records on the email column with the value empty: ''

If you use InnoDB you can have multiple NULL values, but you can not have multiple empty values '' .

Try to clean the empty values with UPDATE users SET email = NULL WHERE email = '' and then create the unique key.