Concurrency Problem in SQL Server

There are four concurrency problem in Sql Server.

1 - Lost Update
2 - Non-Repeatable Read
3 - Dirty Read
4 - Phantom Read

1 - Lost Update

This type of problem occure when two transections modify the same data at the same time and the transection that complete first is lost by the second transection.

2 - Non-Repeatable Read

This type of problem occure when a transection is able to read same row multiple times and get a diffrent value each time.

3 - Dirty Read

This type of problem is a special case of Non-Repeatable Read. This occure if you run a report and get the data which are not commited yet and can be rollbacked by a transection.

4 - Phantom Read

This type of problem occure when you have read a record in first read and when you edit this record then you get the error then the record is not exist. This problem is called Phantom Read.

Regards
Manish