Redgate Data Modeler

4 December 2015

Tip #4 – How to Make a Column Unique

Sometimes there are columns in a table that don’t belong to primary key, but are still unique. To mark them as a unique, you have to create an alternate (unique) key containing it.

Single-column alternate (unique) key

Select the table with the column you want to make a unique. Then, click the Alternate (unique) key tab in the Table properties panel on the right:

Click Add key:

Click the down arrow to show the properties:

Find the column you want to make a unique and add it to the key:

Now, the column is unique:

You can check the table code by clicking the SQL preview button in the top right corner:

Multicolumn alternate (unique) key

Your unique key may have more than one column. To create a multicolumn one, select the table, expand the Alternate (unique) key section on the right, and click Add key:

Add all columns you want to include in your key:

Your multicolumn alternate (unique) key is ready (as seen on the SQL code preview):

Setting an index as unique

You can make an index unique too. Just go to your index:

Click Set next to the Index type field:

And select UNIQUE:

The SQL preview of your unique index looks as follows: