You can set the isolation level of a current connection using the isolation_level database option.

Some interfaces, such as ODBC, allow you to set the isolation level for a connection at connection time. You can reset this level later using the isolation_level database option. See isolation_level option.

You can override any temporary or public settings for the isolation_level database option within individual INSERT, UPDATE, DELETE, SELECT, UNION, EXCEPT, and INTERSECT statements by including an OPTION clause in the statement.