References
Reference NO 1
http://stackoverflow.com/questions/15165243/double-post-entry-into-db-while-using-function
Reference NO 2
http://stackoverflow.com/questions/14334063/duplicate-entry-insert-in-database-when-using-json-encode-method-in-php
Reference NO 3
http://www.sitepoint.com/forums/showthread.php?933890-prevent-duplicate-entries
Reference NO 4
http://forums.eukhost.com/f19/avoiding-duplicate-database-entries-4711/
Reference NO 5
http://forum.kohanaframework.org/discussion/7174/dbinsert-values-execute-inserting-duplicate-entry/p1
Reference NO 6
http://bytes.com/topic/php/answers/833623-how-can-i-avoid-adding-duplicate-entries-into-database-table
Reference NO 7
http://www.inmotionhosting.com/support/edu/website-design/using-php-and-mysql/php-insert-database
Reference NO 8
http://www.html.net/tutorials/php/lesson19.php