• employee
• employee_orgn: federated primary key (employee_id,orgn_id), index 1, 2:orgn_id employees, index
• orgn

explain SELECT DISTINCT
    e.*
FROM
    employee e
        LEFT JOIN
    employee_orgn eo ON eo.employee_id = e.id
        LEFT JOIN
    orgn o ON o.id = eo.orgn_id
WHERE
    e.state != "deleted"
        AND e.state != "hidden"
        AND (o.state != "hidden" OR o.state IS NULL)
ORDER BY e.id DESC

Q:

1. here join joint search, mysql nested loop query to the order of magnitude of 10 to the 8th?
2. Why is there a temporary table, and why the sorting is file sorting
3. Why is the second row an override index
4. would like to explain the explain result and optimize the analysis

Thank you very much ~