为什么使用 Mysql 查询结果不同

Question

I have two queries. No error in these queries just results are different.

Query 1

SELECT * FROM notices
WHERE CURDATE( ) < end_date
OR end_date = NULL
ORDER BY id

Result of Query One:

Query 2

select * from notices
where CURDATE() < end_date or end_date='0000-00-00' 
order by id

Result of Query Two:

Table Structure

Question

My Question is that why query 1 not showing the same results as query 2 showing?

Answer 1

Because NULL is not the same as "0000-00-00"

PD: If you want to set a where clause and select where field is null you should use "WHERE end_date IS NULL", not "WHERE end_date = NULL"

Answer 2

From my understanding NULL is different from 0000-00-00 for Date type.Some developer use 0000-00-00 as a default value. Since both NULL and 0000-00-00 are different, you are seeing two different resultsets.

Check this default date '0000-00-00 00:00:00' or null