Please explain and elaborate 1Dirty reads 2 Nonrepeatable re

Please explain and elaborate 1.Dirty reads 2. Non-repeatable reads 3. Phantom reads for resource locking.

Solution

Answer:

Dirty Read : Here a transaction reads that data which is been written by any other transaction that is not committed yet. Here is the example :

Transaction X begins :

UPDATE STUDENT SET MARKS = 95 WHERE STUDENT ID = \'1337\' ;

Transaction Y begins :

SELECT * FRON STUDENT

Now the transaction Y sees the data which is updated by X, but those updates have not yet been committed.

2. Non-repeatable reads :- This happens when in same transaction , same query gives different results. It happens when the same transaction repeatedly retrieves the data.

Example :

Transaction A begins :

SELECT* FROM STUDENT WHERE STUDENT ID = \'1337\';

Transaction B begins

UPDATE STUDENT MARKS= 98 WHERE STUDENT ID = \'1337\';

Here the transaction B updates the rows viewed by A before transaction A commits.

3. Phantom reads : -

It occurs where in a transaction execute same query more than once.