SQL> --Unique Key
SQL>
SQL>
SQL> create table myTable (
2 a number unique,
3 b number
4 );
Table created.
SQL>
SQL>
SQL> desc
Usage: DESCRIBE [schema.]object[@db_link]
SQL>
SQL> insert into myTable values (4, 5);
1 row created.
SQL> insert into myTable values (2, 1);
1 row created.
SQL> insert into myTable values (2, 1);
insert into myTable values (2, 1)
*
ERROR at line 1:
ORA-00001: unique constraint (SYS.SYS_C004357) violated
SQL> insert into myTable values (9, 8);
1 row created.
SQL> insert into myTable values (6, 9);
1 row created.
SQL> insert into myTable values (null,9);
1 row created.
SQL> insert into myTable values (null,9);
1 row created.
SQL>
SQL> select * from myTable;
A B
---------- ----------
4 5
2 1
9 8
6 9
9
9
6 rows selected.
SQL>
SQL> alter table myTable drop constraint sys_c004357;
Table altered.
SQL>
SQL>
SQL> insert into myTable values (4, 5);
1 row created.
SQL> insert into myTable values (2, 1);
1 row created.
SQL> insert into myTable values (2, 1);
1 row created.
SQL> insert into myTable values (9, 8);
1 row created.
SQL> insert into myTable values (6, 9);
1 row created.
SQL> insert into myTable values (null,9);
1 row created.
SQL> insert into myTable values (null,9);
1 row created.
SQL>
SQL> select * from myTable;
A B
---------- ----------
4 5
2 1
9 8
6 9
9
9
4 5
2 1
2 1
9 8
6 9
A B
---------- ----------
9
9
13 rows selected.
SQL>
SQL> drop table myTable;