The problem of territory realignment (reassigning rows among subscribers) requires special attention, just as in the section Territory realignment in the Contacts example.

You need to write triggers to maintain proper data throughout the installation when territory realignment (reassignment of rows among subscribers) is allowed.

How customers are transferred

This example requires that a customer transfer be achieved by deleting and inserting rows in the Policy table.

To cancel a sales relationship between a customer and a sales representative, a row in the Policy table is deleted. In this case, the Policy table change is properly replicated to the sales representative, and the row no longer appears in their database. However, no change has been made to the Customers table, and so no changes to the Customers table are replicated to the subscriber.

In the absence of triggers, this would leave the subscriber with incorrect data in their Customers table. The same kind of problem arises when a new row is added to the Policy table.

Using triggers to solve the problem

The solution is to write triggers that are fired by changes to the Policy table, which include a special syntax of the UPDATE statement. The special UPDATE statement makes no changes to the database tables, but does make an entry in the transaction log that SQL Remote uses to maintain data in subscriber databases.

A BEFORE INSERT trigger

Here is a trigger that tracks INSERTS into the Policy table, and ensures that remote databases contain the proper data.

CREATE TRIGGER InsPolicy
BEFORE INSERT ON Policy
REFERENCING NEW AS NewRow
FOR EACH ROW
BEGIN
   UPDATE Customers
   PUBLICATION SalesRepData
   SUBSCRIBE BY (
      SELECT rep_key
      FROM Policy
      WHERE cust_key = NewRow.cust_key
      UNION ALL
      SELECT NewRow.rep_key
   )
   WHERE cust_key = NewRow.cust_key;
END;

A BEFORE DELETE trigger

Here is a corresponding trigger that tracks DELETES from the Policy table:

CREATE TRIGGER DelPolicy
BEFORE DELETE ON Policy
REFERENCING OLD AS OldRow
FOR EACH ROW
BEGIN
   UPDATE Customers
   PUBLICATION SalesRepData
   SUBSCRIBE BY (
      SELECT rep_key
      FROM Policy
      WHERE cust_key = OldRow.cust_key
      AND Policy_key <> OldRow.Policy_key
   )
   WHERE cust_key = OldRow.cust_key;
END;

Some of the features of the trigger are the same as in the previous section. The major new features are that the INSERT trigger contains a subquery, and that this subquery can be multi-valued.

Multiple-valued subqueries

The subquery in the BEFORE INSERT trigger is a UNION expression, and can be multi-valued:

...
SELECT rep_key
FROM Policy
WHERE cust_key = NewRow.cust_key
UNION ALL
SELECT NewRow.rep_key
...

The subquery in the BEFORE DELETE trigger is multi-valued:

...
SELECT rep_key
FROM Policy
WHERE cust_key = OldRow.cust_key
AND rep_key <> OldRow.rep_key
...

Notes