How to remove bad characters that are not suitable for utf8 encoding in MySQL?

How to remove bad characters that are not suitable for utf8 encoding in
MySQL?

References

Reference NO 1

http://stackoverflow.com/questions/13657019/how-to-remove-bad-characters-that-are-not-suitable-for-utf8-encoding-in-mysql

Reference NO 2

http://bugs.mysql.com/57877

Reference NO 3

http://www.bluebox.net/about/blog/2009/07/mysql_encoding/

Reference NO 4

http://mysql.rjweb.org/doc.php/charcoll

Reference NO 5

https://confluence.atlassian.com/display/CONFKB/Change+MySQL+Database+Character+Encoding+to+UTF8+During+Server+Migration

Reference NO 6

http://php.net/manual/en/function.utf8-encode.php

Reference NO 7

http://en.wikibooks.org/wiki/Perl_Programming/Unicode_UTF-8

Reference NO 8

http://coding.smashingmagazine.com/2012/06/06/all-about-unicode-utf8-character-sets/