SelectParameters - If Checked Add Where

What im looking to do is put a checkbox on my page and if the box is checked have it add a where clause to the sql statement.

The most i have seen with selectparameters is for it to basically take the value of the given control (or whatever) and dump it in to a query.

In this case what i would like to do is if the box is not checked it has my basic query run Select * from Table

and if the box is checked i would like it to run Select * from table where status='completed'

basically a check box that shows only completed items.

wasnt sure if i could do this with just the sqldatasource control and some selectparameters or if i had to write some code.

 Thanks

Justin