A novice question

I have a blob column in a data window, OLEdatabaseBLOB, that enables me to retrieve, update, and store an MS Word doc.  If I hard code the key value in the key clause, works fine.  If I switch to a variable (e.g., :job_id), it doesn't resolve.  The SQL shows the key value as "?", null.  So here's the dumb question, how do I pass a value to the variable in the key clause?  I've tried doing it several ways through the data window arguments but to no avail.

James