The specific usage of null value in mysql

This article mainly explains "the specific use of null value in mysql". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let Xiaobian take you to learn "the specific usage of null value in mysql"!

NULL is not 0 and cannot be compared. NULL can also be understood as an unknown placeholder.

2, NULL length is NULL, in fact, it is occupied space.

NULL values cannot be manipulated by comparison algorithms, such as =, or.

For NULL values, IS NULL and IS NOT NULL must be used.

examples

mysql> select * from test_class;+----------+--------------+| class_id | class_name |+----------+--------------+| 1 |Class 1, Grade 1|| 2 |Class 1 (2)|| 3 |Class 1 (3)|| 4 |Class 1 (4)|| 5 |Class 2 (1)|| 6 |Class 2, Grade 2|| 7 |Class 2 (3)|| 8 |Class 2 (4)|| 9 |Class 3 (1)|| 10 |Class 3 (2)|| 11 |Class 3, Grade 3|| 12 |Class 3 (4)|| 13 | NULL |+---------+-----------+13 rows in set (0.00 sec) At this point, I believe that everyone has a deeper understanding of "the specific use of null value in mysql", so let's actually operate it! Here is the website, more related content can enter the relevant channels for inquiry, pay attention to us, continue to learn!