如何在MySQL中将默认值设置为NULL?
在MySQL中使用DEFAULT关键字将默认值设置为NULL。让我们首先创建一个-
mysql> create table DemoTable1440 -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(20) DEFAULT NULL, -> StudentAge int DEFAULT NULL -> );
使用insert命令在表中插入一些记录。对于保留为空的值,将插入默认值-
mysql> insert into DemoTable1440(StudentName,StudentAge) values('Chris',21); mysql> insert into DemoTable1440 values(); mysql> insert into DemoTable1440(StudentName) values('David'); mysql> insert into DemoTable1440(StudentAge) values(24);
使用选择显示表中的所有记录-
mysql> select * from DemoTable1440;
这将产生以下输出-
+-----------+-------------+------------+ | StudentId | StudentName | StudentAge | +-----------+-------------+------------+ | 1 | Chris | 21 | | 2 | NULL | NULL | | 3 | David | NULL | | 4 | NULL | 24 | +-----------+-------------+------------+ 4 rows in set (0.00 sec)