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Per ANSI SQL, the four standard isolation levels in order from weakest to strongest are
AREAD COMMITTED, READ UNCOMMITTED, SERIALIZABLE, REPEATABLE READ
BREPEATABLE READ, SERIALIZABLE, READ COMMITTED, READ UNCOMMITTED
CREAD UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE
DSERIALIZABLE, REPEATABLE READ, READ COMMITTED, READ UNCOMMITTED
Answer & Solution
Correct answer: C. READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE
ANSI SQL orders the four levels by what they prevent: READ UNCOMMITTED (nothing), READ COMMITTED (no dirty reads), REPEATABLE READ (no unrepeatable reads), SERIALIZABLE (no phantoms either). Each level prevents everything the weaker ones do, plus one more anomaly.
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