Page 44 of 95
17. How many types of database triggers can be specified on a table ?
What are they ?
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row
affected by the statement.
If WHEN clause is specified, the trigger fires according to the
retruned boolean value.
18. Is it possible to use Transaction control Statements such a
ROLLBACK or COMMIT in Database Trigger ? Why ?
It is not possible. As triggers are defined for each table, if you
use COMMIT of ROLLBACK in a trigger, it affects logical
transaction processing.
19. What are two virtual tables available during database trigger
execution ?
The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only
available.
For triggers related to UPDATE only OLD.column_name NEW.column_name
values only available.
For triggers related to DELETE only OLD.column_name values only
available.
20. What happens if a procedure that updates a column of table X is
called in a database trigger of the same table ?
Mutation of table occurs.
21. Write the order of precedence for validation of a column in a
table ?
I. done using Database triggers.
ii. done using Integarity Constraints.
I & ii.
Exception :
22. What is an Exception ? What are types of Exception ?
Exception is the error handling part of PL/SQL block. The types
are Predefined and user_defined. Some of Predefined execptions are.
CURSOR_ALREADY_OPEN
|
|