Oracle user_contraints表的constraint_type列中的字母代码是什么意思？

select distinct constraint_type from user_constraints; C - C P R U 

似乎P表示主键，R表示外键，对吗？ 什么是U和C？

Answer 1

从12cR1文档 ：

 C - Check constraint on a table P - Primary key U - Unique key R - Referential integrity V - With check option, on a view O - With read only, on a view H - Hash expression F - Constraint that involves a REF column S - Supplemental logging 

Answer 2

 Code Description Acts On Level --------------------------------------------- C Check on a table Column O Read Only on a view Object P Primary Key Object R Referential (Foreign Key) Column U Unique Key Column V Check Option on a view Object