MySQL的运算符
MySQL的运算符主要有 算数运算，比较运算，逻辑运算，位操作运算。
目录：
- 算数运算符
- 比较运算符
- 逻辑运算符
- 位运算符
- 运算符的优先级
算数运算符
例1：创建表temp，定义类型 num(int)字段，插入数值64，对num值进行算数运算
MariaDB [lyshark]> create table temp(num int); Query OK, 0 rows affected (0.01 sec) MariaDB [lyshark]> insert into temp value(64); Query OK, 1 row affected (0.00 sec) MariaDB [lyshark]> select * from temp; +------+ | num | +------+ | 64 | +------+ 1 row in set (0.00 sec) MariaDB [lyshark]> select num,num+10,num-4,num+5-10,num+20.5 from temp; #进行加减运算 +------+--------+-------+----------+----------+ | num | num+10 | num-4 | num+5-10 | num+20.5 | +------+--------+-------+----------+----------+ | 64 | 74 | 60 | 59 | 84.5 | +------+--------+-------+----------+----------+ 1 row in set (0.00 sec) MariaDB [lyshark]> select num,num*2,num/2,num%3 from temp; #进行乘除运算 +------+-------+---------+-------+ | num | num*2 | num/2 | num%3 | +------+-------+---------+-------+ | 64 | 128 | 32.0000 | 1 | +------+-------+---------+-------+ 1 row in set (0.00 sec) MariaDB [lyshark]>
比较运算符
1.等于运算符（=）
使用等于运算符进行相等判断
MariaDB [lyshark]> select 1=1 , 1=0 , '1'=1 , '0.01'=0 , 'a'='a' , (1+1)=(2+2) , NULL=NULL; +-----+-----+-------+----------+---------+-------------+-----------+ | 1=1 | 1=0 | '1'=1 | '0.01'=0 | 'a'='a' | (1+1)=(2+2) | NULL=NULL | +-----+-----+-------+----------+---------+-------------+-----------+ | 1 | 0 | 1 | 0 | 1 | 0 | NULL | +-----+-----+-------+----------+---------+-------------+-----------+ 1 row in set (0.00 sec)
2.全等于运算符（<=>）
这个运算符和=功能相同，但是全等于可以用来判断NULL值，而等于是不能的
MariaDB [lyshark]> select 1<=>0 , 1<=>1 , '1'<=>1 , '0.01' <=> 0 , 'a' <=> 'a' , (10+10)<=>(20+20) , NULL<=>NULL ; +-------+-------+---------+--------------+-------------+-------------------+-------------+ | 1<=>0 | 1<=>1 | '1'<=>1 | '0.01' <=> 0 | 'a' <=> 'a' | (10+10)<=>(20+20) | NULL<=>NULL | +-------+-------+---------+--------------+-------------+-------------------+-------------+ | 0 | 1 | 1 | 0 | 1 | 0 | 1 | +-------+-------+---------+--------------+-------------+-------------------+-------------+ 1 row in set (0.00 sec)