January 2008
Intermediate to advanced
384 pages
8h 1m
English
Content preview from Joe Celko's Thinking in Sets: Auxiliary, Temporal, and Virtual Tables in SQL
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Chapter 17. Triggers for Constraints
THERE IS A myth that triggers have to be used for complex constraints. While there is a place for triggers in a few situations, they are usually avoidable. But more than that, they are procedural code and should be avoided in favor of declarative code that the optimizer can use.
Furthermore, while there is an ANSI/ISO Standard for triggers, most vendors have highly proprietary implementations, so the code will not easily port. In Standard SQL, a trigger name is unique in the whole schema even though it is attached to a particular base table. It is executed before or after an INSERT, UPDATE, and/or DELETE action. The INSTEAD OF trigger is used on VIEWs that would not otherwise be updatable to change the underlying ...
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