selection screen: at selection-screen output

Hello,

I create a parameter of material number on a selection screen. I code under 'AT SELECTION-SCREEN OUTPUT' to select old material number from the DB Table and output the old number on the selection screen. To inquire the old number, the user should first input a material number and press 'Enter'. The old number shows then. How can I replacing 'Enter' with 'Tab' to process the 'AT SELECTION-SCREEN OUTPUT' module. Because there are many other fields should be input by the user, when the cursor is set on the second field, the select statement is processed.

Thanx.