Need to populate combo from SQL Server based on data in grid

Hi. I have a grid that is being populated by a render_sql command. Inside the grid, I need to populate a combo box on each line using SQL Server data. The data in the combo box will be different for each record depending upon the data in a cell. My select statement for the combo box will look like the following:

SELECT WBS FROM billing_items WHERE Item_Number = ‘cell item number’

We are using PHP with DHTMLX. How do I build a combo box for this scenario?