User's Manual

Chapter 7. SQL Remote Design for Adaptive Server Anywhere
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 second part of the UNION is the rep_key value for the new sales
representative dealing with the customer, taken from the INSERT
statement.
♦ The first part of the UNION is the set of existing sales representatives
dealing with the customer, taken from the Policy table.
This illustrates the point that the result set of the subscription query must
be all those sales representatives receiving the row, not just the new sales
representatives.
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
...
♦ The subquery takes rep_key values from the Policy table. The values
include the primary key values of all those sales reps who deal with the
customer being transferred (WHERE cust_key = OldRow.cust_key),
with the exception of the one being deleted (AND rep_key <>
OldRow.rep_key).
This again emphasizes that the result set of the subscription query must
be all those values matched by sales representatives receiving the row
following the DELETE.
Notes ♦ Data in the Customer table is not identified with an individual subscriber
(by a primary key value, for example) and is shared among more than one
subscriber. This allows the possibility of the data being updated in more
than one remote site between replication messages, which could lead to
replication conflicts. You can address this issue either by permissions
(allowing only certain users the right to update the Customer table, for
example) or by adding RESOLVE UPDATE triggers to the database to
handle the conflicts programmatically.
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