How to add an unique constraint or index ?

Click on the table which you want to add the unique constraint. Then, the table's properties panel will appear on the right.

Go to the Indexes group, and click on the add Icon (Figure 2). This will display the Index Properties panel as shown in the Figure 3.

Figure 3. Index properties panel.

Ensure to select Unique index type, and the columns that will be constrained (also the order of the columns). Check below the detailed process.

Animation 1. Adding unique constraint.