MACROMEDIA COLDFUSION MX 61-CFML Informations techniques télécharger pdf (Page 45)

Exercise 3: Designing the database for your application 45

Establishing a relationship between the two tables

When the user selects an event type from the list obtained from reading the eventtypes table, the

correct event type must be saved to the trips table with all the other trip-related data. The

application could store the eventType (for example, mountain climbing) itself into the eventType

column in the trips table. But if the name Mountain Climbing were later shortened to Climbing

in the eventtypes table, new mountain climbing trips would be classified differently than ones

saved before the change. For this reason and to save space in the database, the key to the

eventtypes row (eventTypeID) is stored in the trips table instead.

The two tables are said to have a relationship. This relationship works by matching data in key

fields. In this case, the matching fields consist of a primary key (eventTypeID) from the eventtypes

table, which provides a unique identifier for each record, and a foreign key (eventType) in the trips

table. The foreign key contains the same value as the primary key, pointing to a unique event

type. The following figure shows this relationship:

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 151 152

Pas de commentaire

MACROMEDIA COLDFUSION MX 61-CFML Informations techniques Page 45