引言
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:
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
1. mysql> select 1+2; 2. +-----+ 3. | 1+2 | 4. +-----+ 5. | 3 | 6. +-----+
1. mysql> select 1-2; 2. +-----+ 3. | 1-2 | 4. +-----+ 5. | -1 | 6. +-----+
3、乘
1. mysql> select 2*3; 2. +-----+ 3. | 2*3 | 4. +-----+ 5. | 6 | 6.
4、除
1. mysql> select 2/3; 2. +--------+ 3. | 2/3 | 4. +--------+ 5. | 0.6667 | 6.
5、商
1. mysql> select 10 DIV 4; 2. +----------+ 3. | 10 DIV 4 | 4. +----------+ 5. | 2 | 6.
、取余
1. mysql> select 10 MOD 4; 2. +----------+ 3. | 10 MOD 4 | 4. +----------+ 5. | 2 | 6.
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。
1、等于
mysql> select 2=3; +-----+ | 2=3 | +-----+ | 0 | +-----+ mysql> select NULL = NULL; +-------------+ | NULL = NULL | +-------------+ | NULL | +-------------+
2、不等于
1. mysql> select 2<>3; 2. +------+ 3. | 2<>3 | 4. +------+ 5. | 1 | 6. +------+
3、安全等于
与 = 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
1. mysql> select 2<3; 2. +-----+ 3. | 2<3 | 4. +-----+ 5. | 1 | 6. +-----+
5、小于等于
1. mysql> select 2<=3; 2. +------+ 3. | 2<=3 | 4. +------+ 5. | 1 | 6. +------+
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。
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。
1、按位与
1. mysql> select 3&5; 2. +-----+ 3. | 3&5 | 4. +-----+ 5. | 1 | 6. +-----+
2、按位或
1. mysql> select 3|5; 2. +-----+ 3. | 3|5 | 4. +-----+ 5. | 7 | 6. +-----+
3、按位异或
1. mysql> select 3^5; 2. +-----+ 3. | 3^5 | 4. +-----+ 5. | 6 | 6. +-----+
4、按位取反
mysql> select ~18446744073709551612; +-----------------------+ | ~18446744073709551612 | +-----------------------+ | 3 | +-----------------------+
5、按位右移
1. mysql> select 3>>1; 2. +------+ 3. | 3>>1 | 4. +------+ 5. | 1 | 6. +------+
6、按位左移
mysql> select 3<<1; +------+ | 3<<1 | +------+ | 6 | +------+
