Mysql JOIN优化。

join性能自行百度，google

数据60w+,这里我只测试了一个limit ，

SELECT count(1) FROM (SELECT * FROM tablt1 AS C LIMIT 100000,100) AS C LEFT JOIN table2 AS B ON C.e_id=B.id;

SELECT count(1) FROM tablt1 AS C LEFT JOIN table2 B ON (C.e_id=B.id) LIMIT 100000,100;