If NULL values are involved in Boolean operations, the result will vary depending on the operator type. For AND operator, FALSE takes precedence over NULL. The result can be summarized in a table below:

AND  TRUE FALSE NULL

TRUE true false null

FALSE false false false

NULL null false null

For OR operator, TRUE takes precedence over NULL. The result can be summarized in a table below:

OR TRUE FALSE NULL

TRUE true true true

FALSE true false null

NULL true null null

The tutorial script below shows you that NULL AND FALSE returns FALSE:

IF 0=NULL AND 0=1 PRINT 'NULL AND FALSE returns TRUE'

ELSE PRINT 'NULL AND FALSE does not returns TRUE'

GO

NULL AND FALSE does not returns TRUE

IF NOT (0=NULL AND 0=1)

PRINT 'NULL AND FALSE returns FALSE'

ELSE PRINT 'NULL AND FALSE does not returns FALSE'

GO

NULL AND FALSE returns FALSE