Answer is Serializable ---Highest isolation level and Lowest one is Read Uncommitted
The Isolation level are defined for transaction :
We will see what violation can happen with each isolation level : violation are Dirty read , Non repeatable read, Phantom .
The first one is Read Uncommitted : So here Dirty read , Non repeatable read, Phantom . all are possible
The second One is Read Committed : It reads the data after the another transaction is committed But it doesnt guarantee That the next time it will read the same data value then it will get same old value .. Dirty read--Not possible , Non repeatable read--Possible , Phantom-- Possible .
Third one : Repeated Read : : It reads the data after the another transaction is committed But it guarantee That the next time it will read the same data value then it will get same old value .. Dirty read--Not possible , Non repeatable read--not possible, Phantom-- Possible .
Fourth One is : Serializable : It is highest and toughest isolation level . It will give always Consistent result . It would have schedules equivalent to Serial Schedules .Dirty read--Not possible , Non repeatable read--Possible , Phantom-- Not Possible .
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