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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
Character data types (GLS)
Change the data type

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.

Change the data type

After the table is built, you can use the ALTER TABLE statement to change the data type that is assigned to a column. Although such alterations are sometimes necessary, you should avoid them for the following reasons:

To change a data type, the database server must copy and rebuild the table. For large tables, copying and rebuilding can take a lot of time and disk space.
Some data type changes can cause a loss of information. For example, when you change a column from a longer to a shorter character type, long values are truncated; when you change to a less-precise numeric type, low-order digits are truncated.
Existing programs, forms, reports, and stored queries might also have to be changed.