how to compare similar column names in two tables

I have two tables.

Faculty_Code Text (Table Name Faculty_Details)

Records in the Faculty_Details as follows;

Faculty_Code

Another Table (Table Name Schedule_Details)

Faculty_Code

then in the run mode in the combo box all the Faculty_Code from Faculty_Details( table) will display in the combo box.

in combo box Faculty_Code as follows from the table Faculty_Details.

Then i have one button called View.

when user select Faculty_Code GS (the Gs Faculty_Code is there in the both the table) from the combo box and click the view button.

i want to show the message the select faculty is there.please select different faculty.

how can i show the pop up message using c sharp.