MySQL: How to check if a query is using Index

As the screenshot below, use SQLYod execute the query, look at 'Profiler' tab, 'Possible_keys' and 'key' is null, we know that the query is not using index.

 Another example, as the screenshot below, if the query is using index, we will see index name displayed

Refer: http://www.mysqlperformanceblog.com/2012/11/23/full-table-scan-vs-full-index-scan-performance/