Progress
Embedded SQL-92
Guide and Reference


Introduction

Use NULL values in a database when the value in a column is unknown or when the value is not applicable. For example, if an employee has not been assigned to a department, you might set the department number in the corresponding row to a NULL value.

To illustrate further, suppose the commission column of the employee table is applicable only to sales persons. This column could contain a NULL value for employees from all other departments. Note that a numeric zero is not the same as a NULL value. Similarly, a string of blanks is not the same as a NULL value.

In Progress SQL-92, the default value for a column is NULL unless the column definition contains the DEFAULT clause. A column of any data type can have a NULL value. You can specify that a column of any type not have NULL values by using the NOT NULL clause in the CREATE TABLE statement. Using NULL values is discussed in the following sections.


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