SQL Query to update Item OnHand in SAP B1 2005

hi all,

is it possible to write a Update query in sql to modify item OnHand ? is it possible to do that in SAP B1 for UDF?

i want to create a UDF and the enter value in it should be deducted from the Item OnHand Stock. is there any query is possible to modify the item on hand.

if it is possible then kindly send me the query.

sandip