---
title: MySQL笔记： 编程基础
date: 2017-03-31 21:07:00
updated: 2017-03-31 21:07:00
description: "编程基础"
categories: [个人笔记]
tags: [MySQL, MySQL笔记]
---

```sql
-- 1. 常量
-- 字符串常量
SELECT 'I\'m a student.' AS col1;
-- 时间日期常量 (复合日期时间格式的字符串)
SELECT '2016-08-31' AS '日期','14:32:00' AS '时间';
-- 十六进制
SELECT X'41',X'4d7953514c';
SELECT 0x41,0x4d7953514c;
SELECT HEX(0x4d7953514c);
-- 二进制
SELECT b'111101',b'1',b'11';
-- 布尔值
SELECT TRUE,FALSE;

-- 2. 变量

-- 2.1 会话变量
SET @username = '张三';
SELECT @username AS 'username';
SET @age = 18;
SELECT @username AS '姓名',@age AS '年龄';
SET @age = @age + 1;
SELECT @username AS '姓名',@age AS '年龄';

SELECT @a = 'a';
SELECT @a := 'a';
SELECT @a AS '@a';

SELECT 119 INTO @age;
SELECT @age AS '年龄';

-- 3. 运算符
-- + - * / % DIV
SET @num = 15;
SELECT @num+2,@num-2,@num*2,@num/2,@num%3,@num DIV 3;
-- 时间
SELECT '2016-8-31'+ INTERVAL '3' DAY;
-- 布尔运算
-- > < >= <= <> != is null 
SELECT 'ab' = 'ab','b'>'a',NULL=NULL,NULL IS NULL;
-- 逻辑运算
-- and or xor
SELECT 1 AND 2,2 AND 0,2 AND TRUE,2 AND 'true',1 XOR 2,1 XOR FALSE;
-- 位运算
-- & | ~ >> <<
SELECT b'101' & b'011',5&2,5|2,~5,5^2,5>>2,5<<2;
```