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Old and new values of E are computed 3. The execution state of T is extracted from the stack and T is resumed 47 Trigger semantics Cascading trigger execution is allowed up to a maximum number of triggers in the execution chain When an error occurs rollback of all operations performed by the triggers rollback of the entire transaction The trigger monitors the Inventory table inserts into an audit table the information on the user performing updates on the table the update date and number of updated d tuples The following table is given InventoryAudit UserName, Date, Update Pag.
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Before triggers on E are executed 4. New values are applied to the DB the modification due to E is actually performed Constraints are checked compensative actions may trigger other triggers, hence cause a recursive invocation of the same D M BG execution procedure 46 Trigger semantics Execution algorithm Before triggers cannot modify the database apart from the tuples affected by the triggering statement tuple variables are used cannot trigger other triggers The execution of row and statement triggers with the same mode is in arbitrary order When more triggers are activated on the same event and mode they are executed in creation order Trigger execution is deterministic After triggers triggered by E are executed If any trigger contains an action A which triggers other triggers the same execution procedure is recursively invoked on A 6.
T s execution is suspended and its state is saved into a stack 2. Identify the events which may violate the constraint i. DCId; end if; Update trigger 3 Update trigger 3 Update trigger 3 Update of DCId on S No condition It is always executed update table ES for the degree course where the student was enrolled decrement TotalStudents, or delete tuple if last student update table ES for the degree course where the student is currently enrolled increment TotalStudents, or insert new tuple if first student check if table ES contains the tuple for the degree course NEW.
After statement triggers are executed A mutating table is the table modified by the statement i. Before statement triggers are executed 2. Write the constraint as a SQL predicate It provides a condition for the trigger execution 2. Integrity constraints on tables are checked 4.
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