MySQL 运算符 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|| |<= |小于等于|| |>= |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 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 | +-----------------------+ ``` 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| |&#921;| 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 最低优先级为： :=。 最高优先级为： !、BINARY、 COLLATE。