Changing the same column in two tables at the same time

Question

Hi,
Oracle 10g2
I have 2 tables:
1. tab1 : Stores people info
2. tab2 : Stores people insurance info
Both have an address field.
What I need to do is when tab1.address is updated I want the tab2.address to update automatically and
when tab2.address is updated I want tab1.address to update.
Is there a way to do this using triggers without having these triggers mutate?
Thanks,
Oleg
Edited by: user635344 on Oct 8, 2009 11:04 AM

Answer 1

Hi, Oleg,
Centinul, Toon, Hoek and Peter are right. (It would be unusual if any one of them were wrong.)
The addresses really ought to be in one table.
If you really must have them in two (or more) tables, then don't INSERT or UPDATE addresses direectly into the tables; use a separate stored procedure, not a trigger.
If you really must use a trigger (and this means a trigger on each table), then before each trigger updates the other table, check a flag to see if the current table is being updated because of DML on the other, and, if so, do nothing. If the current table is not being updated because of DML on the other, then set the flag before doing the update.
In the example below, I used a package variable as the flag. You could also use a SYS_CONTEXT or a Global Temporary Table.
CREATE TABLE tab1
(      id    NUMBER
,      addr  VARCHAR2 (25)
DROP TABLE     tab2;
CREATE TABLE tab2
(      id    NUMBER
,      addr  VARCHAR2 (25)
CREATE OR REPLACE PACKAGE pk_x
AS
    -- This package contains no functions or procedures, only 1 variable:
    table_of_origin     varchar2 (30);
END     pk_x;
CREATE OR REPLACE TRIGGER     tab1_aiu
AFTER INSERT OR UPDATE OF addr on tab1
FOR EACH ROW
BEGIN
     IF  pk_x.table_of_origin  IS NULL
     THEN
          pk_x.table_of_origin := 'TAB1';
          UPDATE  tab2
          SET     addr     = :NEW.addr
          WHERE     id     = :NEW.id;
          pk_x.table_of_origin := NULL;
     END IF;
END     tab1_aiu;
CREATE OR REPLACE TRIGGER     tab2_aiu
AFTER INSERT OR UPDATE OF addr on tab2
FOR EACH ROW
BEGIN
     IF  pk_x.table_of_origin  IS NULL
     THEN
          pk_x.table_of_origin := 'TAB2';
          UPDATE  tab1
          SET     addr     = :NEW.addr
          WHERE     id     = :NEW.id;
          pk_x.table_of_origin := NULL;
     END IF;
END     tab1_aiu;
/I made this example as simple as possible. Production code would be a lot more complicated (e.g., checking to see if id was changed).
I tested this using the DML statements below.
The contents of both tables is shown after each statement.
INSERT INTO tab1 (id, addr) VALUES (1, '1 First St.');
      ID_1 ADDR_1                          ID_2 ADDR_2
         1 1 First St.
INSERT INTO tab2 (id, addr) VALUES (1, 'Forstagatan 1');
      ID_1 ADDR_1                          ID_2 ADDR_2
         1 Forstagatan 1                      1 Forstagatan 1
UPDATE        tab1
SET        addr     = 'Primo Place'
WHERE        id     = 1;
      ID_1 ADDR_1                          ID_2 ADDR_2
         1 Primo Place                        1 Primo PlaceThe query that displayed the contents is:
SELECT  tab1.id           AS id_1
,     tab1.addr     AS addr_1
,     tab2.id           AS id_2
,     tab2.addr     AS addr_2
FROM                tab1
FULL OUTER JOIN           tab2     ON     tab1.id     = tab2.id
ORDER BY   NVL (tab1.id, tab2.id);