http://searchsqlserver.techtarget.com/tip/Understanding-NULL-values-in-SQL-ServerA NULL indicates that a value for an entry is not available. This makes a null different from a zero or an empty or blank value. You'll find NULLs valuable when you need to kn

<br />Let us make a experiment .<br /> <br />Create test table<br /> <br />CREATE TABLE TEST<br />(<br />  id INT NULL <br />)<br /><br /><br />INSERT INTO TEST VALUES (1)<br />INSERT INTO TEST VALUES (2)<br />INSERT INTO TEST VALUES (3)<br />