In this query we are updating MRP of OpeningStock table from taking MRP from TEMP_PLU_MRP table.
1. Before executing the query don't forget to check TEMP_PLU_MRP must have distinct PLU_Codes.
2. It is already considered that PLUMaster is having unique PLUs.
3. Always run select query with same conditions like..
4. Avoid unnecessary writes by using this condition..
