MySQL 运算符

本章节我们主要介绍 MySQL 的运算符及运算符的优先级。 MySQL 主要有以下几种运算符:
  • 算术运算符
  • 比较运算符
  • 逻辑运算符
  • 位运算符

算术运算符

MySQL 支持的算术运算符包括:

运算符 作用
+ 加法
- 减法
* 乘法
/ 或 DIV 除法
% 或 MOD 取余

在除法运算和模运算中,如果除数为0,将是非法除数,返回结果为NULL。

1、加

mysql> select 1+2;
+-----+
| 1+2 |
+-----+
|   3 |
+-----+

2、减

mysql> select 1-2;
+-----+
| 1-2 |
+-----+
|  -1 |
+-----+

3、乘

mysql> select 2*3;
+-----+
| 2*3 |
+-----+
|   6 |
+-----+

4、除

mysql> select 2/3;
+--------+
| 2/3    |
+--------+
| 0.6667 |
+--------+

5、商

mysql> select 10 DIV 4;
+----------+
| 10 DIV 4 |
+----------+
|        2 |
+----------+

6、取余

mysql> select 10 MOD 4;
+----------+
| 10 MOD 4 |
+----------+
|        2 |
+----------+

比较运算符

SELECT语句中的条件语句经常要使用比较运算符。通过这些比较运算符,可以判断表中的哪些记录是符合条件的。比较结果为真,则返回 1,为假则返回 0,比较结果不确定则返回 NULL。

符号 描述 备注
= 等于
<>, != 不等于
> 大于
< 小于
<= 小于
>= 大于等于
BETWEEN 在两值之间 >=min&&<=max
NOT BETWEEN 不在两值之间
IN 在集合中
NOT IN 不在集合中
<=> 严格比较两个NULL值是否相等 两个操作码均为NULL时,其所得值为1;而当一个操作码为NULL时,其所得值为0
LIKE 模糊匹配
REGEXP 或 RLIKE 正则式匹配
IS NULL 为空
IS NOT NULL 不为空

1、等于

mysql> select 2=3;
+-----+
| 2=3 |
+-----+
|   0 |
+-----+


mysql> select NULL = NULL;
+-------------+
| NULL = NULL |
+-------------+
|        NULL |
+-------------+

2、不等于

mysql> select 2<>3;
+------+
| 2<>3 |
+------+
|    1 |
+------+

3、安全等于

= 的区别在于当两个操作码均为 NULL 时,其所得值为 1 而不为 NULL,而当一个操作码为 NULL 时,其所得值为 0而不为 NULL。

mysql> select 2<=>3;
+-------+
| 2<=>3 |
+-------+
|     0 |
+-------+


mysql> select null=null;
+-----------+
| null=null |
+-----------+
|      NULL |
+-----------+

        
mysql> select null<=>null;
+-------------+
| null<=>null |
+-------------+
|           1 |
+-------------+

4、小于

mysql> select 2<3;
+-----+
| 2<3 |
+-----+
|   1 |
+-----+

5、小于等于

mysql> select 2<=3;
+------+
| 2<=3 |
+------+
|    1 |
+------+

6、大于

mysql> select 2>3;
+-----+
| 2>3 |
+-----+
|   0 |
+-----+

7、大于等于

mysql> select 2>=3;
+------+
| 2>=3 |
+------+
|    0 |
+------+

8、BETWEEN

mysql> select 5 between 1 and 10;
+--------------------+
| 5 between 1 and 10 |
+--------------------+
|                  1 |
+--------------------+

9、IN

mysql> select 5 in (1,2,3,4,5);
+------------------+
| 5 in (1,2,3,4,5) |
+------------------+
|                1 |
+------------------+

10、NOT IN

mysql> select 5 not in (1,2,3,4,5);
+----------------------+
| 5 not in (1,2,3,4,5) |
+----------------------+
|                    0 |
+----------------------+

11、IS NULL

mysql> select null is NULL;
+--------------+
| null is NULL |
+--------------+
|            1 |
+--------------+

mysql> select 'a' is NULL;
+-------------+
| 'a' is NULL |
+-------------+
|           0 |
+-------------+

12、IS NOT NULL

mysql> select null IS NOT NULL;
+------------------+
| null IS NOT NULL |
+------------------+
|                0 |
+------------------+

        
mysql> select 'a' IS NOT NULL;
+-----------------+
| 'a' IS NOT NULL |
+-----------------+
|               1 |
+-----------------+

13、LIKE

mysql> select '12345' like '12%';
+--------------------+
| '12345' like '12%' |
+--------------------+
|                  1 |
+--------------------+

mysql> select '12345' like '12_';
+--------------------+
| '12345' like '12_' |
+--------------------+
|                  0 |
+--------------------+

14、REGEXP

mysql> select 'beijing' REGEXP 'jing';
+-------------------------+
| 'beijing' REGEXP 'jing' |
+-------------------------+
|                       1 |
+-------------------------+

mysql> select 'beijing' REGEXP 'xi';
+-----------------------+
| 'beijing' REGEXP 'xi' |
+-----------------------+
|                     0 |
+-----------------------+

逻辑运算符

逻辑运算符用来判断表达式的真假。如果表达式是真,结果返回 1。如果表达式是假,结果返回 0。

运算符号 作用
NOT 或 ! 逻辑非
AND 逻辑与
OR 逻辑或
XOR 逻辑异或

1、与

mysql> select 2 and 0;
+---------+
| 2 and 0 |
+---------+
|       0 |
+---------+

        
mysql> select 2 and 1;   
+---------+     
| 2 and 1 |      
+---------+      
|       1 |      
+---------+

2、或

mysql> select 2 or 0;
+--------+
| 2 or 0 |
+--------+
|      1 |
+--------+

mysql> select 2 or 1;
+--------+
| 2 or 1 |
+--------+
|      1 |
+--------+

mysql> select 0 or 0;
+--------+
| 0 or 0 |
+--------+
|      0 |
+--------+

mysql> select 1 || 0;
+--------+
| 1 || 0 |
+--------+
|      1 |
+--------+

3、非

mysql> select not 1;
+-------+
| not 1 |
+-------+
|     0 |
+-------+

mysql> select !0;
+----+
| !0 |
+----+
|  1 |
+----+

4、异或

mysql> select 1 xor 1;
+---------+
| 1 xor 1 |
+---------+
|       0 |
+---------+

mysql> select 0 xor 0;
+---------+
| 0 xor 0 |
+---------+
|       0 |
+---------+

mysql> select 1 xor 0;
+---------+
| 1 xor 0 |
+---------+
|       1 |
+---------+

mysql> select null or 1;
+-----------+
| null or 1 |
+-----------+
|         1 |
+-----------+

mysql> select 1 ^ 0;
+-------+
| 1 ^ 0 |
+-------+
|     1 |
+-------+

位运算符

位运算符是在二进制数上进行计算的运算符。位运算会先将操作数变成二进制数,进行位运算。然后再将计算结果从二进制数变回十进制数。

运算符号 作用
& 按位与
| 按位或
^ 按位异或
! 取反
<< 左移
>> 右移

1、按位与

mysql> select 3&5;
+-----+
| 3&5 |
+-----+
|   1 |
+-----+

2、按位或

mysql> select 3|5;
+-----+
| 3|5 |
+-----+
|   7 |
+-----+

3、按位异或

mysql> select 3^5;
+-----+
| 3^5 |
+-----+
|   6 |
+-----+

4、按位取反

mysql> select ~18446744073709551612;
+-----------------------+
| ~18446744073709551612 |
+-----------------------+
|                     3 |
+-----------------------+

5、按位右移

mysql> select 3>>1;
+------+
| 3>>1 |
+------+
|    1 |
+------+

6、按位左移

mysql> select 3<<1;
+------+
| 3<<1 |
+------+
|    6 |
+------+

运算符优先级

最高优先级为 :=

最低优先级 !BINARYCOLLATE