|1||Read Uncommitted||The user A start a query, then user B made some changes, A will see the changes have not been committed yet (dirty read)|
|2||Read committed||The user A start a query, user B made some changes and commit. But A will not see the changes made by B.|
|3||Repeatable Read||The user A will not see the changes made by B (insert/delete) read the snapshot established by the first read, so 2 queries executed, with 2 different results (phantom read).|
|4||Serializable||All transactions are completely in isolation fashion, executed serially one after another (lock-based concurrency control).|
In Oracle, Repeated Read level is not supported, but in MySQL default isolation level is repeated Read.