删除重复数据 ：
DELETE FROM country_code
WHERE
country_code NOT IN (SELECT
*
FROM
(select max(country_code) from country_code group by country_name )as tmp
);
根据一个表的数据，更新另一个表的数据
UPDATE event_insert as a,country_code as b
SET
a.country_code = b.country_code
WHERE
a.event_country_zh = b.country_name;
SQL
原文：http://www.cnblogs.com/vincent4code/p/5864462.html
