Trigger to keep a single record form a table to a certain status

Question

Hi all.
I have a table which has a "Status" field. I'm trying to accomplish, with a trigger, that the table can only have one record with an "Active" status, so whenever and Insert or Update occurs, if the new value for the "Status" field is "Active", I should update all other records in the table to "Inactive". I've tried several approaches, and managed to make it work on Inserts, but any Updates wll give an error that says that the table is mutating. I've tried to do it on before and after trigger types, without success.
Is there a way to do what I want with a trigger, or do necessarily I have to create an SP that needs to be called before the Insert or Update operation?

Answer 1

Alternatively you can try with as follows:
SQL> create table t as select rownum id, 'Inactive' status from dual connect by level <= 4
  2  union all select 5, 'Active' from dual
  3  /
Table created.
SQL>
SQL> select * from t
  2  /
        ID STATUS
         1 Inactive
         2 Inactive
         3 Inactive
         4 Inactive
         5 Active
SQL> create or replace trigger t_trg
  2     before insert or update
  3     on t
  4     for each row
  5  begin
  6     if (sys_context (
  7                      'userenv',
  8                      'client_info'
  9              ) != 'start transaction'
10      or sys_context (
11                      'userenv',
12                      'client_info'
13              ) is null)
14     then
15             dbms_application_info.set_client_info ('start transaction');
16
17             execute immediate 'update  t@loopback set status = ''Inactive'' where status = ''Act
ive'' and id != :id'
18                     using :new.id;
19
20             dbms_application_info.set_client_info ('end transaction');
21     end if;
22  end t_trg;
23  /
Trigger created.
SQL>
SQL> update t
  2     set status = 'Active'
  3   where id = 2
  4  /
1 row updated.
SQL>
SQL> select * from t
  2  /
        ID STATUS
         1 Inactive
         2 Active
         3 Inactive
         4 Inactive
         5 Inactive
SQL>
SQL> update t
  2     set status = 'Active'
  3   where id = 4
  4  /
1 row updated.
SQL>
SQL> select * from t
  2  /
        ID STATUS
         1 Inactive
         2 Inactive
         3 Inactive
         4 Active
         5 Inactive
SQL>
SQL> insert into t values (6, 'Active')
  2  /
1 row created.
SQL>
SQL> select * from t
  2  /
        ID STATUS
         1 Inactive
         2 Inactive
         3 Inactive
         4 Inactive
         5 Inactive
         6 Active
6 rows selected.
SQL>All you need is the loopback trigger wich I defined as
CREATE DATABASE LINK LOOPBACK
USING '(description=(address=(protocol=beq)(program=/path_to_your_oracle_binary/oracle)))';