Triggers (Visual Database Tools)
Visual Database Tools supports DML Triggers. DML triggers are invoked when a data manipulation language (DML) event takes place in the database. DML events include INSERT, UPDATE, or DELETE statements that modify data in a specified table or view. A DML trigger can query other tables and can include complex Transact-SQL statements. The trigger and the statement that fires it are treated as a single transaction, which can be rolled back from within the trigger. If a severe error is detected (for example, insufficient disk space), the entire transaction automatically rolls back.
Related Items
DML triggers are useful in these ways:
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They can cascade changes through related tables in the database; however, these changes can be executed more efficiently using cascading referential integrity constraints.
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They can guard against malicious or incorrect INSERT, UPDATE and DELETE operations and enforce other restrictions that are more complex than those defined with CHECK constraints.
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Unlike CHECK constraints, DML triggers can reference columns in other tables. For example, a trigger can use a SELECT from another table to compare to the inserted or updated data and to perform additional actions, such as modify the data or display a user-defined error message.
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They can evaluate the state of a table before and after a data modification and take action(s) based on that difference.
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Multiple DML triggers of the same type (INSERT, UPDATE, or DELETE) on a table allow multiple, different actions to take place in response to the same modification statement.
