Oracle PL/SQL Tutorial/System Tables Data Dictionary/all constraints

Get information on all the constraints you have access to using all_constraints.

SQL>
SQL> desc all_constraints;
 Name                   Null?    Type
 -----------------------
 OWNER                  NOT NULL VARCHAR2(30)
 CONSTRAINT_NAME        NOT NULL VARCHAR2(30)
 CONSTRAINT_TYPE                 VARCHAR2(1)
 TABLE_NAME             NOT NULL VARCHAR2(30)
 SEARCH_CONDITION                LONG
 R_OWNER                         VARCHAR2(30)
 R_CONSTRAINT_NAME               VARCHAR2(30)
 DELETE_RULE                     VARCHAR2(9)
 STATUS                          VARCHAR2(8)
 DEFERRABLE                      VARCHAR2(14)
 DEFERRED                        VARCHAR2(9)
 VALIDATED                       VARCHAR2(13)
 GENERATED                       VARCHAR2(14)
 BAD                             VARCHAR2(3)
 RELY                            VARCHAR2(4)
 LAST_CHANGE                     DATE
 INDEX_OWNER                     VARCHAR2(30)
 INDEX_NAME                      VARCHAR2(30)
 INVALID                         VARCHAR2(7)
 VIEW_RELATED                    VARCHAR2(14)
SQL>
SQL> --select * form all_constraints;