Explain Plan for MySQL

The Explain tab displays the information as a grid:

Column
Description
id The SELECT identifier. This is the sequential number of the SELECT within the query.
select_type The type of SELECT, which can be SIMPLE, PRIMARY, UNION, DEPENDENT UNION, UNION RESULT, SUBQUERY, DEPENDENT SUBQUERY, DERIVED, UNCACHEABLE SUBQUERY or UNCACHEABLE UNION.
table The table to which the row of output refers.
type The join type.
possible_keys The possible_keys column indicates which indexes MySQL can choose from use to find the rows in this table.
key The key column indicates the key (index) that MySQL actually decided to use.
key_len

The key_len column indicates the length of the key that MySQL decided to use.

ref

The ref column shows which columns or constants are compared to the index named in the key column to select rows from the table.

rows

The rows column indicates the number of rows MySQL believes it must examine to execute the query.

filtered

The filtered column indicates an estimated percentage of table rows that will be filtered by the table condition.

Extra

This column contains additional information about how MySQL resolves the query.