总结MySQL的一些知识点：MySQL运算符

目录

MySQL 运算符

算术运算符

比较运算符

逻辑运算符

位运算符

运算符优先级

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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

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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 | +----------+

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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<=小于等于>=大于等于BETWEEN在两值之间>=min&&<=maxNOT 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0LIKE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

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

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 | +-----------------------+

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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 | +-------+

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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 | +------+

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运算符优先级

最低优先级为： :=。

最高优先级为： !、BINARY、 COLLATE。