3.3.1.3 Complete design

Based on the discussions for the user and order items, we will create four

database tables. Each table has a set of fields, or column names, where each

field has a data type, a length, and a nullable condition.

  The data type

There are various data types that are available in DB2. We use the

following data types in our database tables:

  varchar: Provides variable length string type

  char: Provides fixed length string type

  date: Provides a date only data type

  timestamp: Provides a date and time up to a microsecond

  int: Provides a whole number type

  The field length

This represents the length of the field, if appropriate. For example, a data

type of char or varchar requires a length, but a data type of date,

timestamp, or int does not.

  The nullable condition

This last attribute, the nullable condition, exists for us to track whether the

field can be left empty or undefined or must be filled in. For example, a    is

a 0 length string; it is not a null string.

The structure of the database that we built is represented by the Entity

Relationship diagram shown in Figure 54.

Chapter 3. Building the Web server

63