How can I create a SQL unique constraint based on 2 columns?

Question

I have a Table like this one:

|UserId   |  ContactID |  ContactName 
---------------------------------------
| 12456   |  Ax759     |  Joe Smith
| 12456   |          


        

Answer 1

You can add unique constraint tou your fields:

ALTER TABLE YourTable
ADD CONSTRAINT UQ_UserId_ContactID UNIQUE(UserId, ContactID)