What do the letter codes in Oracle user_contraints table's constraint_type column stand for?

Question

select distinct constraint_type from user_constraints;

C
-
C
P
R
U

Seems P means primary key and R means foreign key, correct? What are U and C?

Answer 1

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

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