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Chapter 7. SQL Remote Design for Adaptive Server Anywhere
UPDATE table-list
SET column-name = expression, . . .
[ VERIFY (column-name, . . . )
VALUES ( expression, . . .) ]
[ WHERE search-condition ]
The VERIFY clause can be used only if
table-list
consists of a single table.
It compares the values of specified columns to a set of expected values,
which are the values that were present in the publisher database when the
UPDATE statement was applied there. When the VERIFY clause is
specified, only one table can be updated at a time.
The VERIFY clause is useful only for single-row updates. However,
multi-row update statements entered at a database are replicated as a set of
single-row updates by the Message Agent, so this imposes no constraints on
client applications.
Conflict resolution trigger
syntax
The syntax for a RESOLVE UPDATE trigger is as follows:
CREATE TRIGGER trigger-name
RESOLVE UPDATE
OF column-name ON table-name
[ REFERENCING [ OLD AS old_val ]
[ NEW AS new_val ]
[ REMOTE AS remote_val ] ]
FOR EACH ROW
BEGIN
.. .
END
RESOLVE UPDATE triggers fire before each row is updated. The
REFERENCING clause allows access to the values in the row of the table to
be updated (OLD), to the values the row is to be updated to (NEW) and to
the rows that should be present according to the VERIFY clause (REMOTE).
Only columns present in the VERIFY clause can be referenced in the
REMOTE AS clause; other columns produce a “column not found” error.
Using the VERIFY_ALL_
COLUMNS option
The database option VERIFY_ALL_COLUMNS is OFF by default. If it is
set to ON, all columns are verified on replicated updates, and a RESOLVE
UPDATE trigger is fired whenever any column is different. If it is set to
OFF, only those columns that are updated are checked.
Setting this option to ON makes messages bigger, because more information
is sent for each UPDATE.
If this option is set at the consolidated database before remote databases are
extracted, it will be set at the remote databases also.
You can set the VERIFY_ALL_COLUMNS option either for the PUBLIC
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