What does the REPEATABLE READ isolation level mean in the context of transactions, and why is it important for data integrity?

The REPEATABLE READ transaction isolation level guarantees that within a single transaction, all repeated reads of the same data will return the same result. This means that if a transaction has read a certain row, no other transactions can modify or delete that row until the first transaction is completed.

This is important to prevent the phenomenon of "non-repeatable read," where data changes between two reads within the same transaction, potentially leading to inconsistency and errors.

For example, if a banking application transaction reads an account balance, under the REPEATABLE READ level, the balance will not change throughout the transaction, even if other operations attempt to update it.

Thus, REPEATABLE READ ensures data integrity by preventing partial or inconsistent updates during concurrent database operations.