算术运算符
算术运算符只能进行数值的加法，字符串会被当成0处理。
在除法运算和取余运算中，如果除数为0，被视为非法除数，返回结果为null。
+：加法运算
SELECT 'a' + 1 AS addition;
-：减法运算
SELECT 'a' - 1 AS subtraction;
*：乘法运算
SELECT 10 * 9 AS multiplication;
/或DIV：除法运算（DIV是对结果的取整，/是保留小数点后4位）
SELECT 10 DIV 9 AS division;
%或MOD：取余运算
SELECT 10 MOD 9 AS surplus;
比较运算符
=：等于（两个值中，任何一个值为null，结果为null）
SELECT 1 = 2 AS equal;
<>，!=：不等于
SELECT 1 <> 2 AS notEqual;
>：大于
SELECT 'a' > 'b' AS greater;
<：小于
SELECT 'a' < 'b' AS less;
>=：大于等于
SELECT 'a' >= 'b' AS greaterOrEqual;
<=：小于等于
SELECT 'a' <= 'b' AS lessOrEqual;
BETWEEN...AND...：两值之间
SELECT 'b' BETWEEN'a' AND 'c' AS `between`;
NOT BETWEEN...AND...：不处于两值之间
SELECT 'b' NOT BETWEEN 'a' AND 'c' AS notBetween;
IN：在集合中
SELECT 'd' IN ('a', 'b', 'c', 'd', 'e') AS `in`;
NOT IN：不在集合中
SELECT 'd' NOT IN ('a', 'b', 'c', 'd', 'e') AS notIn;
<=>：严格的等于（两个值均为null时，结果为1，只有一个值为null时，结果为0）
SELECT NULL <=> NULL AS equal;
LIKE：模糊匹配
SELECT 'abcde' LIKE 'ab%' AS `like`;
REGEXP，RLIKE：正则匹配
SELECT 'ab111' REGEXP '[0-9]' AS `regexp`;
IS NULL：为空IS NOT NULL：不为空
逻辑运算符
NOT 或 !：逻辑非
SELECT NOT 1 AS `not`;
AND：逻辑与
SELECT 1 AND 0 AS `and`;
OR：逻辑或
SELECT 1 OR 0 AS `or`;
XOR：逻辑异或
SELECT 1 XOR 1 AS `xor`;
位运算符
&：按位与
SELECT 3 & 0 AS `&`;
|：按位或
SELECT 3 | 4 AS `|`;
^：按位异或
SELECT 3 ^ 5 AS `^`;
!：取反
SELECT !0 AS `!`;
<<：左移
SELECT 2 << 1 AS `<<`;
>>：右移
SELECT 3 >> 1 AS `>>`;
运算符优先级
:=优先级最低
