Doubts on constraints

Question

Hi All,
i have table structure like below. i need to create unique constraint on the below 3 columns(combined). Will i be able to create? i am having a doubt because since one column is nullable, can i create unique constraint on all 3 columns?
if yes, then how can i create it?
column_name           Null
col A                   N
col B                   N
col C                   Y

Answer 1

user12133456 wrote:
Hi All,
i have table structure like below. i need to create unique constraint on the below 3 columns(combined). Will i be able to create? i am having a doubt because since one column is nullable, can i create unique constraint on all 3 columns?
if yes, then how can i create it?
column_name           Null
col A                   N
col B                   N
col C                   Y
Yes you can.Unique constraint can contain null but primary not.
SQL> conn test/sm
Connected.
SQL> create table test(col1 number not null,col2 number,coll3 varchar2(50));
Table created.
SQL> alter table test add constraint uk_test unique (col1,col2,col3);
alter table test add constraint uk_test unique (col1,col2,col3)
ERROR at line 1:
ORA-00904: "COL3": invalid identifier
SQL> alter table test add constraint uk_test unique (col1,col2,coll3);
Table altered.
SQL>Edited by: Chinar on Aug 9, 2010 6:54 AM