1、where子句中，and优先级比or高
1 select * from film where film_id < 10 or title like ‘%ARK‘ and length = 50\G
等同于以下查询：
1 select * from film where film_id < 10 or (title like ‘%ARK‘ and length = 50)\G
2、连接列值：concat
1 select concat(‘title: ‘, title, ‘ description: ‘, description) as info from film\G
3、使用case语句
1 select title, 2 case 3 when length <= 70 then ‘short‘ 4 when length > 70 then ‘long‘ 5 end 6 as info from film where film_id = 1\G
4、随机选择n条数据
1 select film_id, title from film order by rand() limit 5\G
5、查找空值
1 select film_id, title from film where title is null\G
null要使用is
6、为空值设定默认值
1 select film_id, coalesce(title, ‘‘) as title from film\G
原文：http://www.cnblogs.com/zcy-backend/p/6805529.html