The Begin Tran

Select the top 1 @ Amount=Amount from [Sells] where ID=@ ID and key=1 order by ID Desc

Business logic (processing is more complex, is about 0.3 seconds)
- update field
The update sells the set key=1
Commit Tran


Due to the large concurrent, there has been no wait for change value, other users have read the record. Cause business processing error.