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Data & Analytics · Intermediate

Non-Repeatable Read

An anomaly in which reading the same row twice in one transaction returns different values because another transaction committed a change in between.

Definition

Non-repeatable reads are allowed under Read Committed and prevented under Repeatable Read and higher levels.

Example

A balance read at the start and end of a report differs because a deposit committed in between.

Exam tip

Non-repeatable read = an existing row's value changed; phantom read = new rows appeared.

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