-- SQLNESS PROTOCOL MYSQL
SELECT read_preference();

+-------------------+
| read_preference() |
+-------------------+
| LEADER            |
+-------------------+

-- SQLNESS PROTOCOL MYSQL
SET read_preference = 'hi';

Failed to execute query, err: MySqlError { ERROR 1235 (42000): (Unsupported): Not supported: Invalid read preference expr hi in set variable statement }

-- SQLNESS PROTOCOL MYSQL
SET read_preference = 'leader';

affected_rows: 0

-- SQLNESS PROTOCOL MYSQL
SELECT read_preference();

+-------------------+
| read_preference() |
+-------------------+
| LEADER            |
+-------------------+