This may be trivial to some, but I thought I’d share it anyway, since the links I found online were a bit hard to dig up about this one: If you need to make a column in a MSSQL table UNIQUE, using SQL Server Management Studio Express, here’s how:

1. Open your tables, right-click on the table you need to make the unique key,  and select ‘Design’ (or Modify):

mssql-unique-step-01

2. Right-click on any of the columns in the righ panel and select ‘Indexes/Keys…’

mssql-unique-step-02

3. On the window that opens up, click ‘Add’ on the bottom-left corner

mssql-unique-step-03

4. A new entry is created on the left. Select it and notice on the right side the ‘Columns’ field. Click the three dots to select the desired column(s), then change the ‘Is Unique’ setting to ‘Yes’.

mssql-unique-step-04

5. Click ‘Close’ and save your table. That’s it!

Note that you will not be able to add this Unique key if the desired column has duplicated data in it.