Question

Transaction T1 updates a row but has not yet committed. Transaction T2 then reads this updated but uncommitted value. If T1 subsequently rolls back, what problem has T2 experienced, and which isolation level prevents this from happening?

Q: Answer-Transaction T1 updates a row but has not yet committed. Transaction T2 then reads this updated but u...

T2 reading a value that T1 has not yet committed and may later roll back is the classic definition of a Dirty Read. This anomaly is prevented starting from the Read Committed isolation level and above, which only permits reads of committed data. Read Uncommitted, by contrast, is the isolation level that specifically permits dirty reads, so it is not the correct answer to prevents.