Using the Dirty Read Option

Use the Dirty Read option to copy rows from the database whether or not there are locks on them. The program that fetches a row places no locks and it respects none. Dirty Read is the only isolation level available to databases that do not implement transaction logging.

This isolation level is most appropriate for static tables that are used for queries of tables where data is not being modified, because it provides no isolation. With Dirty Read, the program might return an uncommitted row that was inserted or modified within a transaction that has subsequently rolled back, or a phantom row that was not visible when you first read the query set, but that materializes in the query set before a subsequent read within the same transaction. (Only the Repeatable Read isolation level prevents access to phantom rows. Only Dirty Read provides access to uncommitted rows from concurrent transactions that might subsequently be rolled back.)

The optional WITH WARNING keywords instruct the database server to issue a warning when DML operations that use the Dirty Read isolation level might return an uncommitted row or a phantom row.