运算操作

运算操作

字符必须是数值类型
+ 加
- 减
* 乘
/ 除
% 取余

mysql> alter table user
-> add age int default 18
-> after name;

mysql> select * from user;

mysql> select name,age,2018-age as start from user 用(2018减去age的值)的结果,as(作为),(字段是start)的值
-> where name="root";
+------+------+-------+
| name | age | start | 字段名为start
+------+------+-------+
| root | 18 | 2000 |
+------+------+-------+

mysql> select name,age,2018-age from user where name="root"; 没有对字段命名，就会默认字段名就是2018-age
+------+------+----------+
| name | age | 2018-age | 默认字段名就是2018-age
+------+------+----------+
| root | 18 | 2000 |
+------+------+----------+