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Data & Analytics · Intermediate

Phantom Read

An anomaly in which re-running a range query returns new or missing rows because another transaction inserted or deleted rows.

Definition

Phantoms are prevented only by Serializable isolation, through range or key-range locks, or by snapshot-based approaches.

Example

COUNT(*) WHERE Status = 'Open' returns 10, then 11 after another session inserts a row.

Exam tip

If the anomaly involves inserted rows matching a WHERE clause, it is a phantom read.

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