What is the difference between the transaction isolation levels Read Committed and Read Uncommitted?

Transaction isolation levels determine how much a transaction can see the changes made by other transactions.

Read Uncommitted:

• A transaction may read data that has been modified but not yet committed by another transaction.
• Dirty reads are possible, where data that may be rolled back is read.

Read Committed:

• A transaction only sees data that has been committed by other transactions.
• Dirty reads are prevented.
• However, non-repeatable reads can occur, where data may change upon re-reading.

In summary:

• Read Uncommitted is the lowest isolation level, allowing dirty reads.
• Read Committed is more strict, preventing dirty reads but allowing non-repeatable reads.

The choice of level depends on data integrity requirements and performance.