A correlation name can be applied to a table in a TableExpression so that its columns can be qualified with that name. If you do not supply a correlation name, the table name qualifies the column name. When you give a table a correlation name, you cannot use the table name to qualify columns. You must use the correlation name when qualifying column names.
No two items in the FROM clause can have the same correlation name, and no correlation name can be the same as an unqualified table name specified in that FROM clause.
For information about the optimizer overrides you can specify, see Tuning Derby.
-- SELECT from a JOIN expression SELECT E.EMPNO, E.LASTNAME, M.EMPNO, M.LASTNAME FROM EMPLOYEE E LEFT OUTER JOIN DEPARTMENT INNER JOIN EMPLOYEE M ON MGRNO = M.EMPNO ON E.WORKDEPT = DEPTNO