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Null Value Handling

  • Article

Visual FoxPro provides support for null values. This support simplifies the task of representing unknown data and makes it easier to work with Microsoft Access or SQL databases that may contain null values.

Null values are:

  • Equal to the absence of any value.

  • Different than zero, the empty string (""), or blank.

  • Sorted ahead of other data.

  • Propagated in calculations and most functions.

Null values affect the behavior of commands and functions, logical expressions, and parameters.

Visual FoxPro support for null values complies with ANSI standards and affects any area of the product where values and expressions are used.

To use null values in

See

Commands and functions

Behavior of Null Values in Commands and Functions

Expressions

Behavior of Null Values in Logical Expressions

Parameters

NULL as a Parameter

Using NULL in Values and Expressions

In Visual FoxPro, you assign the null value programmatically with the .NULL. token or interactively with CTRL+0 in a field. Note that the periods around .NULL. are optional. To detect whether a field or variable contains a null value, or whether an expression evaluates to a null value, use ISNULL( ).

See Also

Concepts

NULL as a Parameter

NULL as a Value

Reference

EMPTY( ) Function

ISBLANK( ) Function

ISNULL( ) Function

Other Resources

Data Manipulation