Derived tables are a sub-query used in the FROM clause.

 

To add a sub-query, right click on the Query Building Area and select Add Derived Table.

 

  

The query building area now contains a object and a corresponding tab representing the newly created derived table. This tab allows you to edit the sub-query the same way as you edit the main query.

 

 

Another way to switch to the sub-query tab is to press the derived table's maximize button.