分2步骤：
1.
select * from user_constraints e where e.table_name='xxx';
2.
select a.constraint_type,a.table_name,a.status, b.table_name,b.column_name,b.constraint_name from user_constraints a
inner join user_cons_columns b
on a.constraint_name = b.constraint_name
where a.r_constraint_name='xxxx'