Which isolation level allows dirty reads?

• A. Read Uncommitted
• B. Read Committed
• C. Repeatable Read
• D. Serializable

Answer: (A)

It tests how transaction isolation levels control whether a query can see data written by another transaction before it’s committed. The level that allows dirty reads is Read Uncommitted. At this level, a transaction may read data that another transaction has modified but not yet committed, so the value read could later be rolled back and disappear—hence a “dirty” read.

Other levels prevent this. Read Committed only reads data that has been committed, so you won’t see uncommitted changes. Repeatable Read ensures that once you read a value, subsequent reads within the same transaction return the same value, avoiding non-repeatable reads. Serializable is the strictest, making transactions appear completely isolated, as if they run one after another, preventing phantom and other anomalies.