What do the letter codes in the Oracle_contraints table mean for the constraint_type table?

Question

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

It seems that P stands for primary key, and R stands for foreign key, right? What is U and C?

Answer 1

 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 

Answer 2

From the 12cR1 documentation :

 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