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SQL> --Unique Key
SQL>
SQL>
SQL> create table myTable (
2 a number unique,
3 b number
4 );
Table created.
SQL>
SQL> desc myTable;
Name Null? Type
----------------------------------------------------------------------------------------------------- -------- --------------------------------------------------------------------
A NUMBER
B NUMBER
SQL>
SQL> -- if a column is not explicitely defined as not null, nulls can be inserted multiple times:
SQL>
SQL> insert into myTable values (4, 5);
1 row created.
SQL> insert into myTable values (4, 1);
insert into myTable values (4, 1)
*
ERROR at line 1:
ORA-00001: unique constraint (SYS.SYS_C004353) 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
9 8
6 9
9
9
SQL>
SQL> drop table myTable;
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