Dirty Read, Non-Repeatable Read and Phantom row

A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction and not yet committed.

A non-repeatable read occurs, when during the course of a transaction, a row is retrieved twice and the values within the row differ between reads.

A phantom read occurs when, in the course of a transaction, two identical queries are executed, and the collection of rows returned by the second query is different from the first. The phantom reads anomaly is a special case of Non-repeatable reads.