MySQL性能分析及explain的使用

EXPLAIN
SELECT
t. USER USER,
CASE t.frost
WHEN 0 THEN
'未冻结'
WHEN 1 THEN
'冻结'
END frost,
CASE seller.frost
WHEN 0 THEN
'未冻结'
WHEN 1 THEN
'冻结'
END frost,
area. NAME aname,
shop. NAME sname,
seller. NAME,
j.ct,
t. USER,
t. NAME iname,
t.mobile
FROM
app_jindou AS j
LEFT JOIN app_seller AS seller on j.id_user = seller.id
LEFT JOIN app_shop AS shop on shop.id = seller.id_shop
LEFT JOIN app_area AS area on area.id = shop.id_area
LEFT JOIN app_instructor AS t on t.id = shop.id_instructor
WHERE
j.id_jdrule IN (1, 2, 3)
AND j.ct >= '2017-03-01 00:00:00'
AND j.ct <= '2017-03-31 23:59:59'
ORDER BY
j.ct ASC