mysql插入数据不全怎么办？

Question

要根据身份证号算年龄

语句：
insert into memberinfo(age)
select
(substring(now(),1,4)-substring(creditcard,7,4))-(substring(creditcard,11,4)-date_format(now(),'%m%d')>0)
from memberinfo

运行以后没有报错
insert into memberinfo(age)
select
(substring(now(),1,4)-substring(creditcard,7,4))-(substring(creditcard,11,4)-date_format(now(),'%m%d')>0)
from memberinfo

> Affected rows: 8388608****

> 时间: 102.076s

****

查询年龄以后，只有一部分是有数字的，其他都为空

请问是什么原因，该怎么办？

Answer 1

你看看select date_format(now(),'%m%d')的值是多少