Query with variable from a dropdown list

Hi all

I need to create a query on ORDR where the user can choose their name from a drop down list at the start of the query.

Eg show all open sales orders where the SlpCode = Adam

Is it possible to provide a dropdown box populated from SlpCode at the start of the query? Do I use a sub SELECT statement within the WHERE statement?

Something along these lines

SELECT T0.[DocNum] FROM ORDR T0 WHERE T0.[SlpCode] = (SELECT T1.[SlpName] FROM OSLP) [%0]

Many thanks in advance