Constraint - at most one record has status 'active' in a table.

Question

Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - Prod
PL/SQL Release 10.2.0.5.0 - Production
CORE 10.2.0.5.0 Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production
Thank in advance. I have a table like this:
CREATE TABLE FIFAPPS.FS_MST_SUPPLIER
SUPL_CODE VARCHAR2(12 BYTE) NOT NULL,
SUPL_STATUS VARCHAR2(12 BYTE) DEFAULT 'ACTIVE' NOT NULL
How to make constraint such that at most one supl_code has supl_status = 'ACTIVE' in the table.
For example:
-- BELOW IS NOT CORRECT AS THERE ARE TWO RECORDS WITH SUPL_STATUS='ACTIVE'
record 1 : (supl_code = '1',SUPL_STATUS='ACTIVE')
record 2 : (supl_code = '2',SUPL_STATUS='NOT ACTIVE')
record 3 : (supl_code = '3',SUPL_STATUS='ACTIVE')
-- -- BELOW IS CORRECT AS THERE IS ONLY ONE RECORD WITH SUPL_STATUS='ACTIVE'
record 1 : (supl_code = '1',SUPL_STATUS='ACTIVE')
record 2 : (supl_code = '2',SUPL_STATUS='NOT ACTIVE')
record 3 : (supl_code = '3',SUPL_STATUS='NOT ACTIVE')
-- -- BELOW IS CORRECT AS THERE IS NO RECORD WITH SUPL_STATUS='ACTIVE'
record 1 : (supl_code = '1',SUPL_STATUS='NOT ACTIVE')
record 2 : (supl_code = '2',SUPL_STATUS='NOT ACTIVE')
record 3 : (supl_code = '3',SUPL_STATUS='NOT ACTIVE')

Answer 1

You cannot refer other rows in check constraint I feel.Ideally these type of validations should happen from your Front-end.
You can try something like below by adding a virtual column..
SQL> CREATE TABLE FS_MST_SUPPLIER
  2  (
  3  SUPL_CODE VARCHAR2(12 BYTE) NOT NULL,
  4  SUPL_STATUS VARCHAR2(12 BYTE) DEFAULT 'ACTIVE' NOT NULL
  5  );
Table created.
--"Add a virtual column. The ELSE part here should be your primary key in the table
SQL> alter table FS_MST_SUPPLIER add dummy_col as
   (case when upper(supl_status) = 'ACTIVE' then 'ACTIVE' else supl_code end);
Table altered.
--"Add a unique constraint on the virtual column.."
SQL> alter table FS_MST_SUPPLIER add constraint cons1 unique(dummy_col);
Table altered.
SQL> insert into FS_MST_SUPPLIER(SUPL_CODE,SUPL_STATUS) values(1,'ACTIVE');
1 row created.
SQL> insert into FS_MST_SUPPLIER(SUPL_CODE,SUPL_STATUS) values(2,'ACTIVE');
insert into FS_MST_SUPPLIER(SUPL_CODE,SUPL_STATUS) values(2,'ACTIVE')
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.CONS1) violated
SQL> insert into FS_MST_SUPPLIER(SUPL_CODE,SUPL_STATUS) values(2,'INACTIVE');
1 row created.
SQL> insert into FS_MST_SUPPLIER(SUPL_CODE,SUPL_STATUS) values(3,'INACTIVE');
1 row created.
SQL> update FS_MST_SUPPLIER set supl_status = 'INACTIVE';
3 rows updated.
SQL> insert into FS_MST_SUPPLIER(SUPL_CODE,SUPL_STATUS) values(5,'ACTIVE');
1 row created.
{code}
Edited by: jeneesh on Oct 17, 2012 3:40 PM
I did not have to use virtual columns or unique function index for any table in my career...