Home
Designing databases
The first step in creating a relational database is to construct a data model, which is a precise, complete definition of the data you want to store. After you prepare your data model, you must implement it as a database and tables. To implement your data model, you first select a data type for each column and then you create a database and tables and populate the tables with data. You can also implement fragmentation strategies and control access to your data.
Designing and Implementing a Database
The Informix® Database Design and Implementation Guide provides information to help you design, implement, and manage your Informix databases. It includes data models that illustrate different approaches to database design and shows you how to use structured query language (SQL) to implement and manage your databases.
Basics of database design and implementation
Select data types
Data types
Null values

Designing databases
The first step in creating a relational database is to construct a data model, which is a precise, complete definition of the data you want to store. After you prepare your data model, you must implement it as a database and tables. To implement your data model, you first select a data type for each column and then you create a database and tables and populate the tables with data. You can also implement fragmentation strategies and control access to your data.
- Designing and Implementing a Database
  The Informix® Database Design and Implementation Guide provides information to help you design, implement, and manage your Informix databases. It includes data models that illustrate different approaches to database design and shows you how to use structured query language (SQL) to implement and manage your databases.

Null values

In most cases, columns in a table can contain null values. A null value means that the value for the column can be unknown or not applicable. For example, in the telephone directory example in Build a relational data model, the anniv column of the name table can contain null values; if you do not know the person's anniversary, you do not specify it. Do not confuse null value with zero or a blank value. For example, the following statement inserts a row into the manufact table of the stores_demo database and specifies that the value for the lead_time column is null:

INSERT INTO manufact VALUES ('DRM', 'Drumm', NULL)

Collection columns cannot contain null elements. Create and use extended data types in Informix describes collection data types.