运算符
运算符
1. 算术运算符
+,-,*,/(DEV),%
没什么注意的点就是常见的运算,不过需要小心null病毒
SELECT 1+2,1*2,1-2,1/2,1DEV2,1%2
FROM DUAL;
2. 比较运算符
2.1 符号描述
= ,> ,< ,>= ,<= ,<>(!=) ,<=>(安全,将null视为正常)
SELECT *
FROM employees
WHERE 1!=2;
SELECT *
FROM employees
WHERE 1<=>NULL;
2.2 SQL语句
IS NULL IS NOT NULL ISNULL() BETWEEN AND(包含边界) IN() LIKE
SELECT *
FROM employees
WHERE ID IS [NOT] NULL;
SELECT *
FROM employees
WHERE ISNULL(ID);
SELECT *
FROM employees
WHERE ID BETWEEN 1001 AND 1010;
SELECT *
FROM employees
WHERE ID IN(1001,1002,1003);
SELECT *
FROM employees
WHERE NAME LIKE 'A'
/*
%表示若干字符,
_表示一个字符,也可用转义字符’\‘,
DESCAPE $,则$将会成为转义字符
2.3 正则运算符(之后学)()ROGEXP
.(一个字符) *(1-9数字)
3. 逻辑运算符
&& || ! XOR
4. 位运算符
& | ^ >> <<
没什么注意的,就是在机器语言上操作,8个bit,&是且,|是并,^相当于求不同,>>右移,一定范围内相当于/2,<<与前者相反;