Oracle Database - Null value

A null is the absence of a value in a column of a row. Nulls indicate missing, unknown, or inapplicable data. A null should not be used to imply any other value, such as zero.

Nulls are stored in the database and require 1 byte to store the length of the column (zero).

If you are calculating an average grade for a student, null values will be ignored in the calculation using standard SQL, giving correct results. (the average of 5, null, 6, 7 is 6 not 4.5)

• What is the data type of NULL ?
• I hate Null
• Toad, the date format with null and decode
• Set Null

SELECT
  CASE NULL
    WHEN NULL
    THEN 'NULL is NULL'
    ELSE 'NULL is Not NULL'
  END AS "Is NULL null?"
FROM
  dual;

Result:

Is NULL null?    
---------------- 
NULL is Not NULL 

• Nulls Indicate Absence of Value