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Database Systems: Design, Implemen...

12th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781305627482

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Chapter
Section
BuyFindarrow_forward

Database Systems: Design, Implemen...

12th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781305627482
Chapter 8, Problem 28P
Textbook Problem
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Create a trigger named trg_line_total to write the LINE_TOTAL value in the LINE table every time you add a new LINE row. (The LINE_TOTAL value is the product of the LINE_UNITS and LINE_PRICE values.)

Program Plan Intro

Trigger:

The trigger is a named set of SQL statement that is executed at the time of data modification or meets some data description.

  • If the stated trigger condition meets up, then the mentioned action in the trigger has been performed.

There are three parts of trigger; they are:

Event:

  • It specifies the change to be made, such as an UPDATE or DELETE of a record.

Condition:

  • It specifies the condition to examine the records about to be affected. For each record, that meets the condition given in the trigger.

Action:

  • The action performed after the start of the trigger.

The syntax to create a trigger is as given below:

CREATE TRIGGER trigger_name

{BEFORE| AFTER|INSTEAD OF} {INSERT|DELETE|UPDATE} ON

table_name

[FOR EACH{ROW|STATEMENT}] [WHEN(condition)]

<triggered SQL statement here>;

Explanation of Solution

Query to create trigger:

CREATE OR REPLACE TRIGGER TRG_LINE_TOTAL

BEFORE INSERT ON LINE

FOR EACH ROW

BEGIN

:NEW.LINE_TOTAL := :NEW.LINE_UNITS * :NEW.LINE_PRICE;

END;

/

Explanation:

  • The above query is used to create a trigger named “TRG_LINE_TOTAL” to add the product values of “LINE_UNITS” and “LINE_PRICE” in the “LINE” table whenever a record is inserted in the “LINE” table...

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Chapter 8 Solutions

Database Systems: Design, Implementation, & Management
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