SQL - Transactions and Data Integrity
In the REPEATABLE READ isolation level, which of the following anomalies is prevented when a transaction reads the same data multiple times?
In the REPEATABLE READ isolation level, which of the following anomalies is prevented when a transaction reads the same data multiple times?
medium📝 query result Q5 of 15
Step-by-Step Solution
Solution:
Step 1: Understand REPEATABLE READ guarantees
REPEATABLE READ ensures that if a transaction reads a row twice, it will see the same data both times, preventing non-repeatable reads.Step 2: Identify anomalies prevented
Dirty reads are prevented by READ COMMITTED and above; phantom reads are prevented only by SERIALIZABLE; lost updates are handled by locking mechanisms.Final Answer:
Non-repeatable reads -> Option CQuick Check:
REPEATABLE READ prevents data changes between reads [OK]
Quick Trick: REPEATABLE READ stops data changes between reads [OK]
Common Mistakes:
- Confusing phantom reads with non-repeatable reads
- Assuming dirty reads are prevented only at SERIALIZABLE
- Mixing lost updates with read anomalies
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