Which indexing is better for simple checking

Which indexing is better for simple checking

References

Reference NO 1

http://www.dreamhost.com/dreamscape/2013/08/19/mysql-checking-the-slow-query-log-and-simple-indexing/

Reference NO 2

https://www.simple-talk.com/sql/learn-sql-server/effective-clustered-indexes/

Reference NO 3

http://docs.oracle.com/cd/B10501_01/appdev.920/a96590/adg06idx.htm

Reference NO 4

http://lifehacker.com/5887848/make-windows-search-a-million-times-more-useful-with-these-simple-tweaks

Reference NO 5

http://www.ncbi.nlm.nih.gov/pubmed/10902785

Reference NO 6

http://stackoverflow.com/questions/3049283/mysql-indexes-what-are-the-best-practises

Reference NO 7

http://www.lullabot.com/blog/article/slow-queries-check-cardinality-your-mysql-indexes

Reference NO 8

http://webmonkeyuk.wordpress.com/2010/09/27/what-makes-a-good-mysql-index-part-2-cardinality/