How do i make two columns of a table not to have same values using My SQL constraints?

How do i make two columns of a table not to have same values using My SQL
constraints?

References

Reference NO 1

http://dev.mysql.com/doc/refman/5.5/en/create-table-foreign-keys.html

Reference NO 2

http://dba.stackexchange.com/questions/39885/can-i-make-sure-two-columns-dont-have-the-same-value

Reference NO 3

http://stackoverflow.com/questions/5594487/mysql-constraining-a-set-of-columns-so-at-least-one-is-not-null

Reference NO 4

http://stackoverflow.com/questions/635937/how-do-i-specify-unique-constraint-for-multiple-columns-in-mysql

Reference NO 5

http://zetcode.com/databases/mysqltutorial/constraints/

Reference NO 6

http://oak.cs.ucla.edu/cs143/project/mysql/constraints.html

Reference NO 7

http://www.w3resource.com/mysql/creating-table-advance/constraint.php

Reference NO 8

http://www.sqlcourse.com/create.html