>I have a grid that displays data from the parts table. However, one of the grid columns uses the following expression as its control source.
>
>iif(seek(parts.customersid,'customers','custid'),customers.name,'')
>
>The expression looks up the customer name in the customers table and displays it in the grid along with the other parts table fields.
>
>How can I order the grid data by customer name?

I would create a cursor that denormalizes the data, and use that for the record source of the grid --

select parts.*, nvl(customers.name, padr('...n/a...', ' ' 40)) as custname ;
   from parts left join customers ;
     on parts.customersid = customers.custid ;
   where...

Then you can index the cursor and display however you want. Pad the CustName with however many spaces needed to match the width of your customers.name field.