Oracle in a Nutshell

Logical Conditions

A logical condition is a condition that can return one of three values—TRUE, FALSE, or UNKNOWN (which, in Oracle, is known as NULL). The three logical conditions supported by Oracle are NOT, AND, and OR.

The results of the NOT conditions for three-state logic (TRUE, FALSE, and UNKNOWN or NULL) are:

NOT TRUE = FALSE

NOT FALSE = TRUE

NOT UNKNOWN = UNKNOWN (NULL)

Table B-2 provides the results of comparisons with combinations of these conditions:

Table B-2. Combinations of logical conditions

Comparison	Value	TRUE	FALSE	UNKNOWN
AND	TRUE	TRUE	FALSE	UNKNOWN
	FALSE	FALSE	FALSE	FALSE
	UNKNOWN	UNKNOWN	FALSE	UNKNOWN
OR	TRUE	TRUE	TRUE	TRUE
	FALSE	TRUE	FALSE	UNKNOWN
	UNKNOWN	TRUE	UNKNOWN	UNKNOWN