– Transaction T1 modifies a row.

– Transaction T2 reads that row before T1 performs a commit.

– If T1 performs a rollback, T2 reads a row that was never committed and is considered to have never existed.

– Transaction T1 reads a row.

– Transaction T2 modifies or deletes that row and performs a commit.

– If T1 attempts to reread the row, it can receive the modified value or discover that the row has been deleted.

– Transaction T1 reads the set of rows N that satisfy some search condition.

– Transaction T2 executes SQL statements that generate one or more rows that satisfy the search condition used by transaction T1.

– If transaction T1 repeats the initial read with the same search condition, it obtains a different collection of rows.