in data assist search, you have the techid column set to filter on the S_techid text box.
instead of hard coding the where cluse to use your select list, why not just delete the S_techid text box, and rename the select list to S_techid?
data assist search will dynamicly create the where clause using form elements that pass a value.
meaning that if your select list default empty option is selected:
<option value="">Show All</option>
that cxolumn will not be included in the where clause.
the way you are doing it now would require hand coding the recordset with an if statement to only include that column in the where clause if a value is passed.