Return a unique list from two columns based on a criteria

Hi all,

I am looking for a formula that will return a unique list from two columns based on if it meets the criteria from another column


Table 1

Department 1------Sub Dept 1
Department 1------Sub Dept 1
Department 1------Sub Dept 2
Department 1------Sub Dept 3
Department 1------Sub Dept 5
Department 2------Sub Dept 1
Department 2------Sub Dept 2

Table 2
Department 1------Sub Dept 1
Department 1------Sub Dept 2
Department 1------Sub Dept 3
Department 1------Sub Dept 4
Department 2------Sub Dept 1
Department 2------Sub Dept 2


Return a unique sub department list for Department 1

Unique List

Sub Dept 1
Sub Dept 2
Sub Dept 3
Sub Dept 4
Sub Dept 5

Hope that makes sense, I know how to get the unique lists with criteria but, am struggling to get it to look at two tables and return one results.

Any help would be very much appriciated.