Oracle外键约束信息的查询

select
    a.table_name 从表, a.column_name 外键列,  b.table_name 主表, b.column_name 被引用列
from
    (
    select
        uc.table_name, ucc.column_name, uc.r_constraint_name
    from
        user_constraints uc
    join
        user_cons_columns ucc
    on
        uc.constraint_name = ucc.constraint_name
    ) a,
    (
    select
        uc.table_name, ucc.column_name, uc.constraint_name
    from
        user_constraints uc
    join
        user_cons_columns ucc
    on
        uc.constraint_name = ucc.constraint_name
    ) b
where
    a.r_constraint_name = b.constraint_name