MySQL explain Query understanding

Using temporary means that MySQL need to use some temporary tables for storing intermediate data calculated when executing your query.

Using filesort is a sorting algorithm where MySQL isn't able to use an index for sorting and therefore can't do the complete sort in memory. Instead it breaks the sort into smaller chunks and then merge the results to get the final sorted data.

Please refer to http://dev.mysql.com/doc/refman/5.0/en/explain-output.html.

I think you might be using an ORDER BY plus some derived table or sub-query. It would be great if you could paste your query and relevant tables/indexes information and the EXPLAIN output.

Syntax:

Explain `MySQL Query`

Example: EXPLAIN SELECT * FROM categoriesG

Example: EXPLAIN EXTENDED SELECT City.Name FROM City JOIN Country ON (City.CountryCode = Country.Code) WHERE City.CountryCode = 'IND' AND Country.Continent = 'Asia'G

Explain followed with your mysql query

Better explained in details here