Using “NULL” as a Character String

Only columns for which NULL was specified in the create table statement and into which you have explicitly entered NULL (no quotes), or into which no data has been entered, contain null values. Avoid entering the character string “NULL” (with quotes) as data for a character column. It can only lead to confusion. Use “N/A”, “none”, or a similar value instead. When you want to enter the value NULL explicitly, do not use single or double quotes.