alter table tablename 增加 add constraint con_name unique(col) 删除 drop constraint com_name[cascade]
select constraint_name,constraint_type from user_constraints where table_name=upper('sxtstu05')
select constraint_name,constraint_type from user_constraints where owner ='SCOTT'
select constraint_name,column_name from user_cons_columns where table_name =upper('tablename')