MIS Test 3 CH16 Triggers

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trigger predicates

INSERTING, UPDATING, DELETING used to check the type of DML statement that caused the trigger to fire

when do you get NULL values for OLD and NEW

OLD - when you use it for a row that is about to be inserted bc it's not there yet NEW - when you use it for a row that is about to be deleted

correlation identifiers

OLD and NEW keywords that work with the values for the columns that are stored in the old row and the new row

how do you tell it when the trigger should be fired?

the BEFORE or AFTER keyword

for compound triggers, what do you code instead of the BEFORE or AFTER keywords?

the FOR keyword bc there can be both BEFORE and AFTER keywords

what follows the UPDATE/INSERT/DELETE part of the block?

the ON statement

what happens when you don't put the FOR EACH ROW thing

the trigger is a statement-level trigger

what can triggers do that constraints cannot?

triggers can be used to enforce rules for data consistency that can't be enforced by constraints

AFTER trigger

triggers used to store information about a statement after it executes

T/F it is possible to create a trigger that's fired when a DDL statement is executed

true

T/F you can call a procedure from inside a trigger

true

T/F you must put COMPOUND TRIGGER to identify that it is in fact a compound trigger

true

when is a trigger fired most of the time?

when an iNSERT, UPDATE, DELETE statement is executed on a table or view

what do you need if you have an UPDATE statement

you need to say UPDATE OF column_name

compound trigger

can contain blocks of PL/SQL that are executed- 1) before the triggering statement is executed 2) before/after the row is modified 3) after the triggering statement has finished executing can also share variables between these blocks of codes

FOR EACH ROW

clause that indicates that the trigger is a row-level trigger and will fire for each row that is modified

SCHEMA

fires the trigger when the DDL event occurs on the specified schema

what does adding WHEN to your FOR EACH ROW clause do

it controls when the trigger is fired put a set of parenthesis with an expression that evaluates to true or false in there

INSTEAD OF trigger

makes the views updateable by executing INSERT, UPDATE, DELETE statements on the underlying table or tables of the view instead of attempting to insert, update, delete data through the view

trigger

named block of PL/SQL code that is executed (fired) automatically when a particular type of SQL statement is executed

you can use a trigger to set a value in a new row that's about to be inserted with a value that's generated by a sequence

pg 513 idk wtf is going on

disable/enable all triggers

ALTER TABLE table_name DISABLE/ENABLE ALL TRIGGERS

syntax to disable/enable a trigger

ALTER TRIGGER trigger_name DISABLE same thing for enable just use ENABLE

renaming a trigger

ALTER TRIGGER trigger_name RENAME TO new_name

DDL events

CREATE, ALTER, DROP, GRANT, REVOKE, DDL

dropping a trigger

DROP TRIGGER trigger_name


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