System Tables Data Dictionary Oracle PLSQL Tutorial

You can get information on your constraints by querying user_constraints.

SQL> desc user_constraints;
 Name                Null?    Type
 --------------------
 OWNER               NOT NULL VARCHAR2(30)
 CONSTRAINT_NAME     NOT NULL VARCHAR2(30)
 CONSTRAINT_TYPE              VARCHAR2(1)   --Constraint type. Set to P, R, C, U, V, or O.
 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)  --Constraint status. Set to ENABLED or DISABLED.
 DEFERRABLE                   VARCHAR2(14) --Whether the constraint is deferrable. Set to DEFERRABLE or NOT DEFERRABLE.
 DEFERRED                     VARCHAR2(9)  --Whether the deferred. Set to IMMEDIATE or DEFERRED.
 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> -- create demo table
SQL> create table myTable(
  2    id           NUMBER(2),
  3    value        NUMBER(6,2)
  4  )
  5  /
Table created.
SQL>
SQL> -- prepare data
SQL> insert into myTable(ID,  value)values (1,9)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (2,2.11)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (3,3.44)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (4,-4.21)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (5,10)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (6,3)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (7,-5.88)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (8,123.45)
  2  /
1 row created.
SQL> insert into myTable(ID,  value)values (9,98.23)
  2  /
1 row created.
SQL>
SQL> select * from myTable
  2  /
        ID      VALUE
---------- ----------
         1          9
         2       2.11
         3       3.44
         4      -4.21
         5         10
         6          3
         7      -5.88
         8     123.45
         9      98.23
9 rows selected.
SQL>
SQL> ALTER TABLE myTable
  2  ADD CONSTRAINT uq UNIQUE (id)
  3  DEFERRABLE INITIALLY DEFERRED;
Table altered.
SQL>
SQL> SELECT
  2   constraint_name, constraint_type, status, deferrable, deferred
  3  FROM user_constraints
  4  WHERE table_name = 'MYTABLE';
CONSTRAINT_NAME                C STATUS   DEFERRABLE     DEFERRED
------------------------------ - -------- -------------- ---------
UQ                             U ENABLED  DEFERRABLE     DEFERRED
SQL>
SQL> -- clean the table
SQL> drop table myTable
  2  /
Table dropped.
SQL>