Question

We have following requirement :

Table1: composite primary key version, id

------------------------------------
version   id     col1  coll2  active
------------------------------------
 1        123    'A'   'B'     'N'
 2        123    'C'   'D'     'Y'
 1        124    'E'   'F'     'Y'

Now for any insert and update on table1 for a given id, a new row should be created with the following attributes (derived by a trigger):

1. Version should be incremented by 1 for given id and
2. most current row should become active (active column is set to Y)

e.g.

INSERT INTO table1(id, col1, col2) VALUES (123, 'X', 'Y');

------------------------------------
version   id     col1  coll2  active
------------------------------------
 1        123    'A'   'B'     'N'
 2        123    'C'   'D'     'N'
 3        123    'X'   'Y'     'Y' 
 1        124    'E'   'F'     'Y'

3rd row is created

UPDATE table1 SET col1 = 'F' WHERE id = 124;

------------------------------------
version   id     col1  coll2  active
------------------------------------
 1        123    'A'   'B'     'N'
 2        123    'C'   'D'     'N'
 3        123    'X'   'Y'     'Y' 
 1        124    'E'   'F'     'N'
 2        124    'F'   'F'     'Y'

last row is created

DELETE FROM dbo.table1 WHERE id = 124;

------------------------------------
version   id     col1  coll2  active
------------------------------------
 1        123    'A'   'B'     'N'
 2        123    'C'   'D'     'N'
 3        123    'X'   'Y'     'Y' 
 1        124    'E'   'F'     'N'
 2        124    'F'   'F'     'N'

all rows for id 124 become inactive.

This seems to be modeling issue , but we are mandated to provide this feature using TABLE1 and supporting triggers.

We are not able to get around modifying the table issue as we need to select max(version)
and then insert into same table, Can anyone please suggest a workaround ?

Answer 1

I don’t like the database design, it’s horrible, but you say you are stuck with it. How about using a view with INSTEAD OF triggers?

1) Rename the table to e.g. TABLE1_BASE

2) Create view TABLE1 as SELECT * FROM TABLE1_BASE

3) Add an INSTEAD OF trigger like this:

create trigger table1_io
instead of insert or update or delete on table1
for each row
begin
  if inserting or updating then 
      update table1_base
      set active = 'N'
      where id = :new.id
      and active = 'y';

      insert into table1_base...;
  elsif deleting then
      update table1_base
      set active = 'N'
      where id = :old.id
      and active = 'y';
  end if;
end;

(Something like that)