Non Repeatable Read is also one of the concurrency problem in SQL Server. And it also causes confusion when two or more user working/reading on the same data.
Let see the situation, how problem occurs?
When one transaction reads the same data twice and another transaction updates that data in between the first and second read of transaction one.
See in the example below:-
As per John, the marks of Robin’s should not be changed from 28 to 42. This is the situation in sql Server called as non repeatable read in SQL Server.