case when then 中判断null的方法

MYSQL 中使用case when then 判断某字段是否为null，和判断是否为字符或数字时的写法不一样，如果不注意，很容易搞错

错误方法:
CASE columnName WHEN null THEN 0 ELSE columnName END
正确方法:

CASE WHEN columnName is null THEN 0 ELSE columnName END

1.SELECT CASE WHEN min(id) IS NULL THEN 0 ELSE min(id) END AS min_id,
   CASE WHEN max(id) IS NULL THEN 0 ELSE max(id) END AS max_id
   FROM stat_user WHERE  stat_time between 2016102310 and 2016122410


2.select ifnull(min(id),0),ifnull(max(id),0) FROM stat_user WHERE  stat_time between 2016102310 and 2016122410

用ifnull这个函数效率会更高一些！