NULL
Syntax
<NULL-Constant> := 'NULL'
Description
Like in SQL-databases, NULL is the constant representing an undefined value for all types. NULL is the only value having the type All (which is a subtype of all other types), so you might it at any position and for any argument of a function.
Understanding the behavior of NULL and of functions with NULL-arguments is very important for database- and OLAP-systems. E.g. if your reports queries data out of a database, the database will return NULL for the value not being stored inside their tables (for example, when no turnaround was stored for a specific date). The CUBE-function then will also return NULL for this values and all functions working with this value will have to deal with this NULL-value.
The most functions also return NULL if any of their parameters is NULL because there is no possible calculation for a valid return-value. But some functions exists especially for the treatment of NULL-values, the most important functions are ISNULL, EXISTS, and ZERO.
Examples
Amount( Time:Dec/2004 )
Results to NULL if there is no amount stored for December 2004
DIV( NULL, 5 )
Always returns NULL (impossible to calculate)
See also
EXISTS, ISNULL, ZERO
