Table Sample:
SQL> desc orders ; Name Null? Type ----------------------------------------- -------- ---------------------------- ORDER_ID NOT NULL NUMBER(12) ORDER_DATE DATE CUSTOMER_ID NOT NULL NUMBER(6) ORDER_TOTAL NUMBER(8,2) SALES_REP_ID NUMBER(6)
1. In-line
alter table orders modify ORDER_DATE not null ;
'NOT NULL Can only be created by in-line mode.
alter table orders modify ORDER_DATE null ;
'NOT NULL Can only be droped by in-line mode.
alter table orders modify ORDER_DATE unique ;
alter table orders modify constraint SYS_C0011140 disable ;
alter table orders modify constraint SYS_C0011140 enable ;
alter table orders drop constraint SYS_C0011138 ;
2. Out-of-line
alter table orders add constraint UN_ORDER_DATE unique(order_date) ;
alter table orders disable constraint UN_ORDER_DATE ;
alter table orders enable constraint UN_ORDER_DATE ;
alter table orders drop constraint UN_ORDER_DATE ;
3.Query
select * from user_constraints where table_name='ORDERS' ;