MySQL指南之SQL语句基础
2024-05-06 09:54:24
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零、结构化查询语言：SQL(Structured Query Language)
DDL 数据定义语言 管理库，表
DML 数据操作语言 增删改查
DCL 数据控制语言 数据控制，权限访问等
准备活动：创建库和表
CREATE DATABASE datatype;
USE datatype;CREATE TABLE type_number(
type CHAR(12),
byte TINYINT UNSIGNED,
range_singed VARCHAR(20),
range_unsinged VARCHAR(20),
info VARCHAR(40)
);
目前状态：
mysql> SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| datatype |
| information_schema |
| mycode |
| mysql |
| performance_schema |
| seckill |
+--------------------+ mysql> USE datatype;
Database changedmysql> SHOW TABLES;
+--------------------+
| Tables_in_datatype |
+--------------------+
| type_number |
+--------------------+mysql> DESC type_number;
+----------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+---------------------+------+-----+---------+-------+
| type | char(12) | YES | | NULL | |
| byte | tinyint(3) unsigned | YES | | NULL | |
| range_singed | varchar(20) | YES | | NULL | |
| range_unsinged | varchar(20) | YES | | NULL | |
| info | varchar(40) | YES | | NULL | |
+----------------+---------------------+------+-----+---------+-------+
一、DML 数据库记录操作 LEVEL 1
LEVEL 1先简单掌握一下下面的用法
MySQL基础操作LEVER1.png
1、记录的插入操作
INSERT INTO <表名> (属性,...) VALUES (值,...),...;
|-- 插入一条数据 INSERT INTO <表名> (属性,...) VALUES (值,...);
INSERT INTO
type_number(type,byte,range_singed,range_unsinged,info)
VALUES
('TINYINT',1,'-2⁷ ~ 2⁷-1','0 ~ 2⁸-1','很小整数');|-- 查询所有 SELECT * FROM <表名>;
mysql> SELECT * FROM type_number;
+---------+------+----------------+----------------+--------------+
| type | byte | range_singed | range_unsinged | info |
+---------+------+----------------+----------------+--------------+
| TINYINT | 1 | -2⁷ ~ 2⁷-1 | 0 ~ 2⁸-1 | 很小整数 |
+---------+------+----------------+----------------+--------------+|-- 你也可以一次，插入多条数据
INSERT INTO
type_number(type,byte,range_singed,range_unsinged,info)
VALUES
('TINYINT',1,'-2⁷ ~ 2⁷-1','0 ~ 2⁸-1','很小整数'),
('SMALLINT',2,'-2¹⁶ ~ 2¹⁶-1','0 ~ 2¹⁶-1','小整数'),
('MEDIUMINT',3,'-2²⁴ ~ 2²⁴-1','0 ~ 2²⁴-1','中等整数'),
('INT',4,'-2³² ~ 2³²-1','0 ~ 2³²-1','标准整数'),
('BIGINT',8,'-2⁶⁴ ~ 2⁶⁴-1','0 ~ 2⁶⁴-1','大整数');mysql> SELECT * FROM type_number;
+-----------+------+----------------------+----------------+--------------+
| type | byte | range_singed | range_unsinged | info |
+-----------+------+----------------------+----------------+--------------+
| TINYINT | 1 | -2⁷ ~ 2⁷-1 | 0 ~ 2⁸-1 | 很小整数 |
| TINYINT | 1 | -2⁷ ~ 2⁷-1 | 0 ~ 2⁸-1 | 很小整数 |
| SMALLINT | 2 | -2¹⁶ ~ 2¹⁶-1 | 0 ~ 2¹⁶-1 | 小整数 |
| MEDIUMINT | 3 | -2²⁴ ~ 2²⁴-1 | 0 ~ 2²⁴-1 | 中等整数 |
| INT | 4 | -2³² ~ 2³²-1 | 0 ~ 2³²-1 | 标准整数 |
| BIGINT | 8 | -2⁶⁴ ~ 2⁶⁴-1 | 0 ~ 2⁶⁴-1 | 大整数 |
+-----------+------+----------------------+----------------+--------------+
2、记录的更新操作
UPDATE <表名> SET 属性 = 值,... WHERE 条件;
UPDATE type_number
SET
info='微型整数'
WHERE type = 'TINYINT';mysql> SELECT * FROM type_number;
+-----------+------+----------------------+----------------+--------------+
| type | byte | range_singed | range_unsinged | info |
+-----------+------+----------------------+----------------+--------------+
| TINYINT | 1 | -2⁷ ~ 2⁷-1 | 0 ~ 2⁸-1 | 微型整数 |
| TINYINT | 1 | -2⁷ ~ 2⁷-1 | 0 ~ 2⁸-1 | 微型整数 |
| SMALLINT | 2 | -2¹⁶ ~ 2¹⁶-1 | 0 ~ 2¹⁶-1 | 小整数 |
| MEDIUMINT | 3 | -2²⁴ ~ 2²⁴-1 | 0 ~ 2²⁴-1 | 中等整数 |
| INT | 4 | -2³² ~ 2³²-1 | 0 ~ 2³²-1 | 标准整数 |
| BIGINT | 8 | -2⁶⁴ ~ 2⁶⁴-1 | 0 ~ 2⁶⁴-1 | 大整数 |
+-----------+------+----------------------+----------------+--------------+
3.记录的删除操作
DELETE FROM <表名> WHERE 条件;
|--- 删除操作
DELETE FROM type_number
WHERE type = 'TINYINT';mysql> SELECT * FROM type_number;
+-----------+------+----------------------+----------------+--------------+
| type | byte | range_singed | range_unsinged | info |
+-----------+------+----------------------+----------------+--------------+
| SMALLINT | 2 | -2¹⁶ ~ 2¹⁶-1 | 0 ~ 2¹⁶-1 | 小整数 |
| MEDIUMINT | 3 | -2²⁴ ~ 2²⁴-1 | 0 ~ 2²⁴-1 | 中等整数 |
| INT | 4 | -2³² ~ 2³²-1 | 0 ~ 2³²-1 | 标准整数 |
| BIGINT | 8 | -2⁶⁴ ~ 2⁶⁴-1 | 0 ~ 2⁶⁴-1 | 大整数 |
+-----------+------+----------------------+----------------+--------------+
4.记录的查询操作
SELECT 属性,... FROM <表名> WHERE 条件;
mysql>
SELECT
type,range_unsinged
FROM type_number
WHERE byte>=4;
+--------+----------------+
| type | range_unsinged |
+--------+----------------+
| INT | 0 ~ 2³²-1 |
| BIGINT | 0 ~ 2⁶⁴-1 |
+--------+----------------+
二、图片表pic (LEVER 2)
这个是用来记录图片信息的表，数据准备过程详见番外篇：
[番外]-练习MySQL没素材？来一波字符串操作
MySQL查询LEVER2.png
1.建表语句
CREATE TABLE pic(id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,pic_path VARCHAR(120) NOT NULL,pic_length INT UNSIGNED DEFAULT 0,pic_mime TINYINT UNSIGNED,pic_width SMALLINT UNSIGNED,pic_height SMALLINT UNSIGNED);|--- id 为主键 自增长
|--- pic_path表示名字，不定长度 ，给个VARCHAR 120 吧，差不多够用吧
|--- 图片文件大小不会非常大，给个INT足够了 ， 给个默认值 0
|--- pic_mime 0 表示 image/png 1表示 image/jpeg 给个最小的
|--- pic_width和pic_height也不会非常大，无符号SMALLINT足够
2.查询操作 AS 的作用
|-- 查询高大于1200像素的记录，使用AS 来 临时更改查询输出的属性名(不会改变实际记录)
mysql>
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height>1200;+----------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------+--------+--------+
| 30000X20000.jpg | 30000 | 20000 |
| 3000X2000.jpg | 3000 | 2000 |
| ecNKedygCmSjTWWF.jpg | 700 | 1352 |
| gtQiXnRfkvvTLinw.jpg | 2880 | 2025 |
| HXqqASHJETSlvpnc.jpg | 3600 | 2400 |
| ndbMXlwKuCpiiVqC.jpg | 1701 | 2268 |
| screen.png | 1080 | 1920 |
| XQWGrglfjGVuJfzJ.jpg | 1200 | 1696 |
+----------------------+--------+--------+
3.查询是属性可参与运算
|-- CONCAT函数用于连接字符串 注意：\需要转义
mysql>
SELECT
CONCAT('E:\\SpringBootFiles\\imgs\\',pic_path) AS 绝对路径,
pic_width * pic_height AS '像素点个数'
FROM pic
WHERE pic_height>1200;+----------------------------------------------+-----------------+
| 绝对路径 | 像素点个数 |
+----------------------------------------------+-----------------+
| E:\SpringBootFiles\imgs\30000X20000.jpg | 600000000 |
| E:\SpringBootFiles\imgs\3000X2000.jpg | 6000000 |
| E:\SpringBootFiles\imgs\ecNKedygCmSjTWWF.jpg | 946400 |
| E:\SpringBootFiles\imgs\gtQiXnRfkvvTLinw.jpg | 5832000 |
| E:\SpringBootFiles\imgs\HXqqASHJETSlvpnc.jpg | 8640000 |
| E:\SpringBootFiles\imgs\ndbMXlwKuCpiiVqC.jpg | 3857868 |
| E:\SpringBootFiles\imgs\screen.png | 2073600 |
| E:\SpringBootFiles\imgs\XQWGrglfjGVuJfzJ.jpg | 2035200 |
+----------------------------------------------+-----------------+
4.WHERE条件的千变万化
MySQL的WHERE.png
4.1: 条件与 -- AND 和 &&
条件必须全部满足
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height>1200 AND
pic_width > 1500;+----------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------+--------+--------+
| 30000X20000.jpg | 30000 | 20000 |
| 3000X2000.jpg | 3000 | 2000 |
| gtQiXnRfkvvTLinw.jpg | 2880 | 2025 |
| HXqqASHJETSlvpnc.jpg | 3600 | 2400 |
| ndbMXlwKuCpiiVqC.jpg | 1701 | 2268 |
+----------------------+--------+--------+|--- AND 效果等于 &&
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height>1200 &&
pic_width > 1500;
4.2: 条件或 -- OR 和 ||
条件满足一个即可
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height>1200 OR
pic_width > 1500;+----------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------+--------+--------+
| 30000X20000.jpg | 30000 | 20000 |
| 3000X2000.jpg | 3000 | 2000 |
| ecNKedygCmSjTWWF.jpg | 700 | 1352 |
| gtQiXnRfkvvTLinw.jpg | 2880 | 2025 |
| HXqqASHJETSlvpnc.jpg | 3600 | 2400 |
| ndbMXlwKuCpiiVqC.jpg | 1701 | 2268 |
| screen.png | 1080 | 1920 |
| XQWGrglfjGVuJfzJ.jpg | 1200 | 1696 |
+----------------------+--------+--------+|--- OR 效果等于 ||
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height>1200 ||
pic_width > 1500;
4.3: 条件非 -- NOT 和 !
对条件取反
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE NOT pic_height < 1200; +----------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------+--------+--------+
| 30000X20000.jpg | 30000 | 20000 |
| 3000X2000.jpg | 3000 | 2000 |
| ecNKedygCmSjTWWF.jpg | 700 | 1352 |
| gtQiXnRfkvvTLinw.jpg | 2880 | 2025 |
| HXqqASHJETSlvpnc.jpg | 3600 | 2400 |
| ndbMXlwKuCpiiVqC.jpg | 1701 | 2268 |
| screen.png | 1080 | 1920 |
| XQWGrglfjGVuJfzJ.jpg | 1200 | 1696 |
+----------------------+--------+--------+
4.4: 散点匹配IN(v1,v2,v3,...)
符合v1,v2,v3,...之一可匹配
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height IN (1696,2268); +----------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------+--------+--------+
| ndbMXlwKuCpiiVqC.jpg | 1701 | 2268 |
| XQWGrglfjGVuJfzJ.jpg | 1200 | 1696 |
+----------------------+--------+--------+
4.5: 区间匹配BETWEEN v1 AND v2
v1,v2之间可匹配
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_height BETWEEN 1696 AND 2268; +----------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------+--------+--------+
| 3000X2000.jpg | 3000 | 2000 |
| gtQiXnRfkvvTLinw.jpg | 2880 | 2025 |
| ndbMXlwKuCpiiVqC.jpg | 1701 | 2268 |
| screen.png | 1080 | 1920 |
| XQWGrglfjGVuJfzJ.jpg | 1200 | 1696 |
+----------------------+--------+--------+
4.6：模糊查询：LIKE
'%'匹配任意多个字符,'_'匹配任意单个字符
mysql>
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_path LIKE 'androi%'; +----------------------------------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+----------------------------------------------+--------+--------+
| android\008525ebc2b7d434070e74c00841a30f.png | 544 | 544 |
| android\054d98e2d96dc42d9b2b036126fccf49.png | 544 | 544 |
| android\05baf2d03651d1110d7a403f14aee877.png | 544 | 544 |
| android\0655e07d6717847489cd222c9c9e0b1d.png | 500 | 500 |
| android\079c4cb46c95b2365b5bc5150e7d5213.png | 544 | 544 |
| android\07a4dc9b4b207cb420a71cbf941ad45a.png | 544 | 544 |
| android\07abb7972a5638b53afa3b5eb98b19c1.png | 500 | 500 |......mysql>
SELECT
pic_path AS 路径 ,
pic_width AS '宽/px',
pic_height AS '高/px'
FROM pic
WHERE pic_path LIKE 'p_em%';+--------------------------------------------+--------+--------+
| 路径 | 宽/px | 高/px |
+--------------------------------------------+--------+--------+
| poem\世界·绽放.jpg | 1148 | 712 |
| poem\我爱你，是火山岩的缄默.jpg | 690 | 397 |
| poem\枝·你是树的狂舞.jpg | 500 | 333 |
| poem\海与鹿王.jpg | 799 | 499 |
| poem\游梦人·诗的诞生.jpg | 800 | 444 |
| poem\珊瑚墓地.jpg | 1104 | 719 |
+--------------------------------------------+--------+--------+
4.7:比较符号= != < > <= >=
小学生都知道的，就不废话了，查看一下小于10Kb的图片
mysql>
SELECT
pic_path AS 路径 ,
pic_length AS '大小/byte'
FROM pic
WHERE pic_length < 10*1024;+----------------------------------------------+-------------+
| 路径 | 大小/byte |
+----------------------------------------------+-------------+
| 30X20.jpg | 10158 |
| android\613f2b8f0eaa8f63bedce9781527c9ab.png | 4001 |
| android\94b5c41232f9761403890c09c2b1aae3.png | 4001 |
| android\d3fd676f224f0734beb48d0c0d2f4e66.png | 4001 |
| udp发送与接收消息_控制台.png | 9184 |
+----------------------------------------------+-------------+
5. GROUP BY分组查询
会先排序，再列出
|--- GROUP BY
SELECT
pic_mime AS "类型",
avg(pic_length) AS '平均大小/byte' ,
count(pic_length) AS '总数量/个' ,
min(pic_length) AS '最小值/byte' ,
max(pic_length) AS '最大值/byte' ,
sum(pic_length) AS '总和/byte'
FROM pic
GROUP BY pic_mime;+--------+-------------------+---------------+----------------+----------------+-------------+
| 类型 | 平均大小/byte | 总数量/个 | 最小值/byte | 最大值/byte | 总和/byte |
+--------+-------------------+---------------+----------------+----------------+-------------+
| 0 | 141518.8734 | 229 | 4001 | 829338 | 32407822 |
| 1 | 2133272.8000 | 60 | 10158 | 116342886 | 127996368 |
+--------+-------------------+---------------+----------------+----------------+-------------+
6.结果集筛选：HAVING
现在查询宽高比在1.1和1.3之间的图片
|-- 如果用WHERE 来查询 感觉有点不优雅
SELECT
pic_path AS 路径 ,
pic_width/pic_height AS '宽高比'
FROM pic
WHERE pic_width/pic_height > 1.1 && pic_width/pic_height<1.3; +------------------------------------------------------------------+-----------+
| 路径 | 宽高比 |
+------------------------------------------------------------------+-----------+
| dQXbnTRjUdNxhiyl.jpg | 1.2308 |
| JsXHWmKqOlziKmeA.jpg | 1.2600 |
| logo\android\Android原生绘图之让你了解View的运动.png | 1.2884 |
| 洛天依.jpg | 1.1990 |
+------------------------------------------------------------------+-----------+|-- AS 相当于将列取了变量，对结果集再进行筛选用HAVING,用WHERE则报错，找不到列
SELECT
pic_path AS 路径 ,
pic_width/pic_height AS ratio
FROM pic
HAVING ratio > 1.1 && ratio <1.3;+------------------------------------------------------------------+--------+
| 路径 | ratio |
+------------------------------------------------------------------+--------+
| dQXbnTRjUdNxhiyl.jpg | 1.2308 |
| JsXHWmKqOlziKmeA.jpg | 1.2600 |
| logo\android\Android原生绘图之让你了解View的运动.png | 1.2884 |
| 洛天依.jpg | 1.1990 |
+------------------------------------------------------------------+--------+
7.结果排序：ORDER BY
按照ratio将序排列
SELECT
pic_path AS 路径 ,
pic_width/pic_height AS ratio
FROM pic
HAVING ratio > 1.1 && ratio <1.3;
ORDER BY ratio DESC +------------------------------------------------------------------+--------+
| 路径 | ratio |
+------------------------------------------------------------------+--------+
| dQXbnTRjUdNxhiyl.jpg | 1.2308 |
| JsXHWmKqOlziKmeA.jpg | 1.2600 |
| logo\android\Android原生绘图之让你了解View的运动.png | 1.2884 |
| 洛天依.jpg | 1.1990 |
+------------------------------------------------------------------+--------+
8.控制条目数：LIMIT
|-- 偏移一条，取两条
SELECT
pic_path AS 路径 ,
pic_width/pic_height AS ratio
FROM pic
HAVING ratio > 1.1 && ratio <1.3
ORDER BY ratio DESC LIMIT 1,2;+----------------------+--------+
| 路径 | ratio |
+----------------------+--------+
| JsXHWmKqOlziKmeA.jpg | 1.2600 |
| dQXbnTRjUdNxhiyl.jpg | 1.2308 |
+----------------------+--------+
三、子查询 (LEVER 3)
1.查询大于平均尺寸的图片 -- WHERE
|--- 出现在其他SQL语句内的SELECT语句
|--- 子查询必须在()内
|--- 增删改查都可以进行子查询,返回：标量，行，列或子查询
|-- 1-1：查出图片平均大小
SELECT
ROUND(AVG(pic_length),2) AS '平均大小'
FROM pic;+--------------+
| 平均大小 |
+--------------+
| 555031.80 |
+--------------+
1 row in set (0.00 sec)|-- 1-2：在用WHERE 筛选
SELECT
pic_path AS 路径 ,
pic_length AS '大小/byte'
FROM pic
WHERE pic_length > 555031.80;+----------------------------------------------+-------------+
| 路径 | 大小/byte |
+----------------------------------------------+-------------+
| 30000X20000.jpg | 116342886 |
| 3000X2000.jpg | 3404969 |
| android\12284e5f7197d8be737fa967c8b00fbe.png | 829338 |
| android\594665add495ac9da8b6bbee1c63f1b8.png | 598974 |
| android\7cc97458727e23f7d161b8a1a7c6b453.png | 559420 |
| android\cbb1524f5ab4266698f3a6fc2992ccae.png | 829338 |
| android\d52539b1b508a594d1f2865037ff50c5.png | 598974 |
| android\f07ddfe5a103e4a024e14e2569f1d70e.png | 829338 |
| android\f0d1e7713d5557a8f9c74c9904843e09.png | 559420 |
| bg.png | 688207 |
| gtQiXnRfkvvTLinw.jpg | 771187 |
| poem\珊瑚墓地.jpg | 984472 |
| XoazFNMQROveEPQn.jpg | 795364 |
+----------------------------------------------+-------------+|--- 也就是将一个语句包在WHERE 条件里
SELECT
pic_path AS 路径 ,
pic_length AS '大小/byte'
FROM pic
WHERE pic_length > (SELECT ROUND(AVG(pic_length),2) FROM pic
);
2.查出每种类型的最新插入的图片 -- WHERE
SELECT
pic_path AS 路径 ,
pic_mime AS 类型
FROM pic
WHERE id IN (SELECT max(id)FROM pic GROUP BY pic_mime
);+------------------+--------+
| 路径 | 类型 |
+------------------+--------+
| 洛天依.jpg | 1 |
| 虚拟机栈.png | 0 |
+------------------+--------+
3.FROM子查询 -- FROM
SELECT
id,
pic_path AS 路径 ,
pic_length AS '大小/byte'
FROM pic
WHERE id>=10&&id<=15
ORDER BY pic_length DESC;+----+----------------------------------------------+-------------+
| id | 路径 | 大小/byte |
+----+----------------------------------------------+-------------+
| 15 | android\0f3bf63796ac370a08ee97b056b0587b.png | 178849 |
| 14 | android\0951ef0be68f0c498ca34ffcd7fc7faa.png | 175842 |
| 11 | android\079c4cb46c95b2365b5bc5150e7d5213.png | 86996 |
| 10 | android\0655e07d6717847489cd222c9c9e0b1d.png | 53764 |
| 12 | android\07a4dc9b4b207cb420a71cbf941ad45a.png | 46270 |
| 13 | android\07abb7972a5638b53afa3b5eb98b19c1.png | 43360 |
+----+----------------------------------------------+-------------+|--- 将查询结果当做一张表，再查询操作
SELECT
id,路径 FROM (SELECT id, pic_path AS 路径 , pic_length AS '大小/byte' FROM pic WHERE id>=10&&id<=15 ORDER BY pic_length DESC
) AS result
WHERE `大小/byte` < 59999;+----+----------------------------------------------+
| id | 路径 |
+----+----------------------------------------------+
| 10 | android\0655e07d6717847489cd222c9c9e0b1d.png |
| 12 | android\07a4dc9b4b207cb420a71cbf941ad45a.png |
| 13 | android\07abb7972a5638b53afa3b5eb98b19c1.png |
+----+----------------------------------------------+
四、连接查询
0.创建关联表
首先连接查询要多张表，现在建一个
mime_type的表
|--- 建表
CREATE TABLE mime_type(mime_id SMALLINT UNSIGNED PRIMARY KEY,mime_info CHAR(24));|--- 插入数据
INSERT INTO mime_type(mime_id,mime_info) VALUES
(0,'image/png'),
(1,'image/jpeg'),
(2,'image/svg+xml'),
(3,'video/mp4'),
(4,'text/plain');|--- 效果
mysql> select * from mime_type;
+---------+---------------+
| mime_id | mime_info |
+---------+---------------+
| 0 | image/png |
| 1 | image/jpeg |
| 2 | image/svg+xml |
| 3 | video/mp4 |
| 4 | text/plain |
+---------+---------------+|-- 为了说明问题，pic表添加一条测试数据：pic_mime = 8 也就是 mime_type表找不到时
INSERT INTO pic(pic_path,pic_length,pic_mime,pic_width,pic_height) VALUES('test.jpg',100,8,300,200);
1.内连接查询 INNER JOIN
SELECT 待查属性 FROM 表1 INNER JOIN 表2 ON 条件 WHERE 条件
SELECT id, pic_path AS 路径 , mime_type.mime_info AS 类型 , pic_length
FROM pic INNER JOIN mime_type
ON pic.pic_mime = mime_type.mime_id
ORDER BY id DESC LIMIT 4;+-----+------------------+------------+------------+
| id | 路径 | 类型 | pic_length |
+-----+------------------+------------+------------+
| 289 | 虚拟机栈.png | image/png | 63723 |
| 288 | 统一返回.png | image/png | 29485 |
| 287 | 洛天依.jpg | image/jpeg | 42117 |
| 286 | 标记整理.png | image/png | 29288 |
+-----+------------------+------------+------------+
2.左连接查询 : LEFT JOIN
保持左表的记录完整性，右表查不到就摆 NULL
SELECT id, pic_path AS 路径 , mime_type.mime_info AS 类型 , pic_length
FROM pic LEFT JOIN mime_type
ON pic.pic_mime = mime_type.mime_id
ORDER BY id DESC LIMIT 4;+-----+------------------+------------+------------+
| id | 路径 | 类型 | pic_length |
+-----+------------------+------------+------------+
| 290 | test.jpg | NULL | 100 |
| 289 | 虚拟机栈.png | image/png | 63723 |
| 288 | 统一返回.png | image/png | 29485 |
| 287 | 洛天依.jpg | image/jpeg | 42117 |
+-----+------------------+------------+------------+
3. 右(外)连接查询 :RIGHT JOIN
保持右表的记录完整性，左表查不到就摆 NULL
SELECT id, pic_path AS 路径 , mime_type.mime_info AS 类型 , pic_length
FROM pic RIGHT JOIN mime_type
ON pic.pic_mime = mime_type.mime_id
ORDER BY id LIMIT 8;+------+--------------------------------------+---------------+------------+
| id | 路径 | 类型 | pic_length |
+------+--------------------------------------+---------------+------------+
| NULL | NULL | text/plain | NULL |
| NULL | NULL | video/mp4 | NULL |
| NULL | NULL | image/svg+xml | NULL |
| 1 | 30000X20000.jpg | image/jpeg | 116342886 |
| 2 | 3000X2000.jpg | image/jpeg | 3404969 |
| 3 | 300X200.jpg | image/jpeg | 99097 |
| 4 | 30X20.jpg | image/jpeg | 10158 |
| 5 | 6dc9e8455c47d964e1a8a4ef04cf9477.jpg | image/jpeg | 236254 |
+------+--------------------------------------+---------------+------------+
4. 全(外)连接 (伪):使用UNION
MySQL不支持全外连接，所以只能采取关键字UNION来联合左、右连接的方法
UNION : 将若干条sql的查询结果集合并成一个。UNION ALL不会覆盖相同结果
SELECT id, pic_path AS 路径 , mime_type.mime_info AS 类型 , pic_length
FROM pic LEFT JOIN mime_type ON pic.pic_mime = mime_type.mime_id
UNION(
SELECT id, pic_path AS 路径 , mime_type.mime_info AS 类型 , pic_length
FROM pic RIGHT JOIN mime_type ON pic.pic_mime = mime_type.mime_id
)
ORDER BY id DESC;+------+------------------------------------------------------------------------------------+---------------+------------+
| id | 路径 | 类型 | pic_length |
+------+------------------------------------------------------------------------------------+---------------+------------+
| 290 | test.jpg | NULL | 100 |
| 289 | 虚拟机栈.png | image/png | 63723 |
| 288 | 统一返回.png | image/png | 29485 |
| 287 | 洛天依.jpg | image/jpeg | 42117 |
...
| 3 | 300X200.jpg | image/jpeg | 99097 |
| 2 | 3000X2000.jpg | image/jpeg | 3404969 |
| 1 | 30000X20000.jpg | image/jpeg | 116342886 |
| NULL | NULL | text/plain | NULL |
| NULL | NULL | video/mp4 | NULL |
| NULL | NULL | image/svg+xml | NULL |
+------+------------------------------------------------------------------------------------+---------------+------------+
5. UNION小测试
CREATE TABLE a(
id CHAR(4),
num INT
);INSERT INTO a(id,num) VALUES
('a',4),('b',6),('c',2),('d',8);CREATE TABLE b(
id CHAR(4),
num INT
);
INSERT INTO b(id,num) VALUES
('b',8),('c',7),('d',3),('e',18);mysql> SELECT * FROM a; mysql> SELECT * FROM b;
+------+------+ +------+------+
| id | num | | id | num |
+------+------+ +------+------+
| a | 4 | | b | 8 |
| b | 6 | | c | 7 |
| c | 2 | | d | 3 |
| d | 8 | | e | 18 |
+------+------+ +------+------+ SELECT id,sum(num) FROM
(SELECT * FROM a
UNION ALL
SELECT * FROM b) as temp
GROUP BY id;+------+----------+
| id | sum(num) |
+------+----------+
| a | 4 |
| b | 14 |
| c | 9 |
| d | 11 |
| e | 18 |
+------+----------+
六、DDL 建库/表
1、关于操作数据库
SHOW DATABASES; # 显示所有的数据库
SHOW CREATE DATABASE <数据库名> # 查看数据库创建信息
USE <数据库名>; # 使用数据库
CREATE DATABASE <数据库名> [CHARACTER SET <字符集>]; # 创建一个将的数据库指定字符集
ALTER DATABASE <数据库名> CHARACTER SET <字符集>; # 修改数据库字符集
DROP DATABASE <数据库名>; # 传说中的删库跑路
SELECT DATABASE(); # 查看当前选中的数据库
2.显示数据库信息
SHOW TABLES; # 展示当前数据库中的表
SHOW TABLES FROM mysql # 展示指定数据库中的表
DESC <表名>; # 查看表结构
SHOW COLUMNS FROM <表名>; # 查看表结构
3.创建表
|-- UNSIGNED 无符号 AUTO_INCREMENT 自增长
|-- ZEROFILL 前面自动填 0 , 默认 UNSIGNED
CREATE TABLE create_test(id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,code TINYINT(5) ZEROFILL DEFAULT 0 );INSERT INTO create_test(code) VALUES (5);INSERT INTO create_test VALUES (); #默认值测试mysql> SELECT * FROM create_test;
+----+-------+
| id | code |
+----+-------+
| 1 | 00005 |
| 2 | 00000 |
+----+-------+
4.为表增加属性
ALTER TABLE <表名> ADD 属性信息 [AFTER 属性] ;
|-- 看一下当前表结构mysql> DESC create_test;
+-------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
+-------+------------------------------+------+-----+---------+----------------+mysql> ALTER TABLE create_test ADD age SMALLINT UNSIGNED NOT NULL;
mysql> DESC create_test;
+-------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
+-------+------------------------------+------+-----+---------+----------------+|-- AFTER可将属性排在指定属性之后(强迫症专用)
|-- ALTER TABLE create_test ADD password VARCHAR(32) AFTER id;
mysql> ALTER TABLE create_test ADD password VARCHAR(32) AFTER id;
mysql> DESC create_test;
+----------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| password | varchar(32) | YES | | NULL | |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
+----------+------------------------------+------+-----+---------+----------------+|-- 一次添加多个属性
ALTER TABLE create_test ADD (aaa VARCHAR(32), bbb VARCHAR(32),ccc VARCHAR(32));
mysql> DESC create_test;
+----------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| password | varchar(32) | YES | | NULL | |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
| aaa | varchar(32) | YES | | NULL | |
| bbb | varchar(32) | YES | | NULL | |
| ccc | varchar(32) | YES | | NULL | |
+----------+------------------------------+------+-----+---------+----------------+
5.为表删除属性
ALTER TABLE <表名> DROP 属性
ALTER TABLE create_test DROP aaa,DROP bbb,DROP ccc;mysql> DESC create_test;
+----------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| password | varchar(32) | YES | | NULL | |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
+----------+------------------------------+------+-----+---------+----------------+
6.修改属性的类型
ALTER TABLE <表名> MODIFY 属性 属性类型 [FIRST];
|-- 把password改成VARCHAR(40)
ALTER TABLE create_test MODIFY password VARCHAR(40);
mysql> DESC create_test;
+----------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| password | varchar(40) | YES | | NULL | |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
+----------+------------------------------+------+-----+---------+----------------+|-- 将某个属性移到最顶
ALTER TABLE create_test MODIFY password VARCHAR(40) FIRST;
+----------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------------------+------+-----+---------+----------------+
| password | varchar(40) | YES | | NULL | |
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
+----------+------------------------------+------+-----+---------+----------------+
7.修改表的属性名
ALTER TABLE <表名> CHANGE 原属性 新属性 新属性类型;
mysql> ALTER TABLE create_test CHANGE password pw varchar(40);
mysql> DESC create_test;
+-------+------------------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------------------+------+-----+---------+----------------+
| pw | varchar(40) | YES | | NULL | |
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| code | tinyint(5) unsigned zerofill | YES | | 00000 | |
| age | smallint(5) unsigned | NO | | NULL | |
+-------+------------------------------+------+-----+---------+----------------+
8.修改表名
方式一：
ALTER TABLE 旧表名 RENAME 新表名;
方式二：RENAME TABLE 旧表名 TO 新表名;
ALTER TABLE create_test RENAME 阿姆斯特朗回旋加速喷气式阿姆斯特朗炮;
mysql> SHOW TABLES;
+--------------------------------------------------------+
| Tables_in_datatype |
+--------------------------------------------------------+
| 阿姆斯特朗回旋加速喷气式阿姆斯特朗炮 |
| a |
| b |
| mime_type |
| pic |
| type_number |
+--------------------------------------------------------+RENAME TABLE 阿姆斯特朗回旋加速喷气式阿姆斯特朗炮 TO toly;mysql> SHOW TABLES;
+--------------------+
| Tables_in_datatype |
+--------------------+
| a |
| b |
| mime_type |
| pic |
| toly |
| type_number |
+--------------------+
SQL 的基础就这样 , 下篇见
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