SET Qty= Qty+1
I just can't help to wonder what it is you really want to do. You example doesn't make sense: one time you talk about hd_spare_detail the next time about hd_spare_details. Is that a typo or are two different tables involved?
Can you explain - like you would explain to a total stranger who doesn't know what you are doing or why you are doing it - again what you want to do and why. Also provide some example data. If you have two tables, one to read from the other to update. Give their definitions (DDL) and some example data for both. Also give the data you want to have in all those tables at the end.
With kind regards . . . . . SQL Server 2000/2005/2012
Grabel's Law: 2 is not equal to 3 -- not even for very large values of 2. Pat Phelan's Law: 2 very definitely CAN equal 3 -- in at least two programming languages