作者Attilax ， EMAIL:1466519819@qq.com
来源：attilax的专栏
地址：http://blog.csdn.net/attilax
select SQL_NO_CACHE *,(
SELECT
LEFT (fecye, 1)
FROM
cyefenbyao force index(i_hezi)
WHERE
cyefenbyao.hezi = rit
limit 1
) AS rit_cye
FROM
(
select
max( gaopinzi.HEZI) hezi,
LEFT (hezi, 1) AS lft,
RIGHT (hezi, 1) AS rit
FROM
gaopinzi
WHERE
LENGTH(hezi) = 6
group by HEZI
limit 30000
) AS t2
要1S,改成join 0.5S..
select SQL_NO_CACHE
t2.* ,LEFT (fecye, 1) as t1
FROM
(
SELECT
max(gaopinzi.HEZI) hezi,
LEFT (hezi, 1) AS lft,
RIGHT (hezi, 1) AS rit
FROM
gaopinzi
WHERE
LENGTH(hezi) = 6
GROUP BY
HEZI
LIMIT 30000
) AS t2
left join cyefenbyao
on cyefenbyao.hezi = t2.rit
