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