MySQL指南之SQL語句基礎

MySQL SQL · 發表 2019-03-17 19:00:00

摘要：個人所有文章整理在此篇，將陸續更新收錄: 知無涯，行者之路莫言終（我的程式設計之路）零、結構化查詢語言：SQL(Structured Query Language) DDL 資料定義語言管理庫，表 DML 資料操作語言增刪改查 DCL 資料控制語言資料...

個人所有文章整理在此篇，將陸續更新收錄: 知無涯，行者之路莫言終（我的程式設計之路）

零、結構化查詢語言：SQL(Structured Query Language)

DDL 資料定義語言 管理庫，表
DML 資料操作語言 增刪改查 
DCL 資料控制語言 資料控制，許可權訪問等

準備活動：建立庫和表

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)
);

目前狀態：

mysql> SHOW DATABASES;
+--------------------+
| Database|
+--------------------+
| datatype|
| information_schema |
| mycode|
| mysql|
| performance_schema |
| seckill|
+--------------------+

mysql> USE datatype;
Database changed

mysql> 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 資料庫記錄操作 `LEVEL 1`

LEVEL 1先簡單掌握一下下面的用法

MySQL基礎操作LEVER1.png

1、記錄的插入操作

INSERT INTO <表名> (屬性,...) VALUES (值,...),...;

|-- 插入一條資料 INSERT INTO <表名> (屬性,...) VALUES (值,...);
INSERT INTO 
type_number(type,byte,range_singed,range_unsinged,info) 
VALUES
('TINYINT',1,'-2⁷ ~ 2⁷-1','0 ~ 2⁸-1','很小整數');

|-- 查詢所有 SELECT * FROM <表名>;
mysql> SELECT * FROM type_number;
+---------+------+----------------+----------------+--------------+
| type| byte | range_singed| range_unsinged | info|
+---------+------+----------------+----------------+--------------+
| TINYINT |1 | -2⁷ ~ 2⁷-1| 0 ~ 2⁸-1| 很小整數|
+---------+------+----------------+----------------+--------------+

|-- 你也可以一次，插入多條資料
INSERT INTO 
type_number(type,byte,range_singed,range_unsinged,info) 
VALUES
('TINYINT',1,'-2⁷ ~ 2⁷-1','0 ~ 2⁸-1','很小整數'),
('SMALLINT',2,'-2¹⁶ ~ 2¹⁶-1','0 ~ 2¹⁶-1','小整數'),
('MEDIUMINT',3,'-2²⁴ ~ 2²⁴-1','0 ~ 2²⁴-1','中等整數'),
('INT',4,'-2³² ~ 2³²-1','0 ~ 2³²-1','標準整數'),
('BIGINT',8,'-2⁶⁴ ~ 2⁶⁴-1','0 ~ 2⁶⁴-1','大整數');

mysql> SELECT * FROM type_number;
+-----------+------+----------------------+----------------+--------------+
| type| byte | range_singed| range_unsinged | info|
+-----------+------+----------------------+----------------+--------------+
| TINYINT|1 | -2⁷ ~ 2⁷-1| 0 ~ 2⁸-1| 很小整數|
| TINYINT|1 | -2⁷ ~ 2⁷-1| 0 ~ 2⁸-1| 很小整數|
| SMALLINT|2 | -2¹⁶ ~ 2¹⁶-1| 0 ~ 2¹⁶-1| 小整數|
| MEDIUMINT |3 | -2²⁴ ~ 2²⁴-1| 0 ~ 2²⁴-1| 中等整數|
| INT|4 | -2³² ~ 2³²-1| 0 ~ 2³²-1| 標準整數|
| BIGINT|8 | -2⁶⁴ ~ 2⁶⁴-1| 0 ~ 2⁶⁴-1| 大整數|
+-----------+------+----------------------+----------------+--------------+

2、記錄的更新操作

UPDATE <表名> SET 屬性 = 值,... WHERE 條件;

UPDATE type_number 
SET 
info='微型整數'
WHERE type = 'TINYINT';

mysql> SELECT * FROM type_number;
+-----------+------+----------------------+----------------+--------------+
| type| byte | range_singed| range_unsinged | info|
+-----------+------+----------------------+----------------+--------------+
| TINYINT|1 | -2⁷ ~ 2⁷-1| 0 ~ 2⁸-1| 微型整數|
| TINYINT|1 | -2⁷ ~ 2⁷-1| 0 ~ 2⁸-1| 微型整數|
| SMALLINT|2 | -2¹⁶ ~ 2¹⁶-1| 0 ~ 2¹⁶-1| 小整數|
| MEDIUMINT |3 | -2²⁴ ~ 2²⁴-1| 0 ~ 2²⁴-1| 中等整數|
| INT|4 | -2³² ~ 2³²-1| 0 ~ 2³²-1| 標準整數|
| BIGINT|8 | -2⁶⁴ ~ 2⁶⁴-1| 0 ~ 2⁶⁴-1| 大整數|
+-----------+------+----------------------+----------------+--------------+

3.記錄的刪除操作

DELETE FROM <表名> WHERE 條件;

|--- 刪除操作
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| 小整數|
| MEDIUMINT |3 | -2²⁴ ~ 2²⁴-1| 0 ~ 2²⁴-1| 中等整數|
| INT|4 | -2³² ~ 2³²-1| 0 ~ 2³²-1| 標準整數|
| BIGINT|8 | -2⁶⁴ ~ 2⁶⁴-1| 0 ~ 2⁶⁴-1| 大整數|
+-----------+------+----------------------+----------------+--------------+

4.記錄的查詢操作

SELECT 屬性,... FROM <表名> WHERE 條件;

mysql> 
SELECT 
type,range_unsinged 
FROM type_number 
WHERE byte>=4;
+--------+----------------+
| type| range_unsinged |
+--------+----------------+
| INT| 0 ~ 2³²-1|
| BIGINT | 0 ~ 2⁶⁴-1|
+--------+----------------+

二、圖片表pic `(LEVER 2)`

這個是用來記錄圖片資訊的表，資料準備過程詳見番外篇：

[番外]-練習MySQL沒素材？來一波字串操作

MySQL查詢LEVER2.png

1.建表語句

CREATE TABLE pic(
id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
pic_pathVARCHAR(120)NOT NULL,
pic_lengthINT UNSIGNEDDEFAULT 0,
pic_mime TINYINT UNSIGNED,
pic_width SMALLINT UNSIGNED,
pic_height SMALLINT UNSIGNED
 );

|--- id 為主鍵 自增長
|--- pic_path表示名字，不定長度 ，給個VARCHAR 120 吧，差不多夠用吧
|--- 圖片檔案大小不會非常大，給個INT足夠了 ， 給個預設值 0 
|--- pic_mime 0 表示 image/png1表示 image/jpeg 給個最小的
|--- pic_width和pic_height也不會非常大，無符號SMALLINT足夠

2.查詢操作 `AS` 的作用

|-- 查詢高大於1200畫素的記錄，使用AS 來 臨時更改查詢輸出的屬性名(不會改變實際記錄)
mysql> 
SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height>1200;

+----------------------+--------+--------+
| 路徑| 寬/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.查詢是屬性可參與運算

|-- CONCAT函式用於連線字串注意：\需要轉義 
mysql> 
SELECT 
CONCAT('E:\\SpringBootFiles\\imgs\\',pic_path) AS 絕對路徑,
pic_width * pic_height AS '畫素點個數' 
FROM pic 
WHERE pic_height>1200;

+----------------------------------------------+-----------------+
| 絕對路徑| 畫素點個數|
+----------------------------------------------+-----------------+
| 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` 條件的千變萬化

MySQL的WHERE.png

4.1: 條件 `與` -- `AND` 和 `&&`

條件必須全部滿足

SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height>1200 AND 
pic_width > 1500;

+----------------------+--------+--------+
| 路徑| 寬/px| 高/px|
+----------------------+--------+--------+
| 30000X20000.jpg|30000 |20000 |
| 3000X2000.jpg|3000 |2000 |
| gtQiXnRfkvvTLinw.jpg |2880 |2025 |
| HXqqASHJETSlvpnc.jpg |3600 |2400 |
| ndbMXlwKuCpiiVqC.jpg |1701 |2268 |
+----------------------+--------+--------+

|--- AND 效果等於 &&
SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height>1200 && 
pic_width > 1500;

4.2: 條件 `或` -- `OR` 和 `||`

條件滿足一個即可

SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height>1200 OR 
pic_width > 1500;

+----------------------+--------+--------+
| 路徑| 寬/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 效果等於 || 
SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height>1200 ||
pic_width > 1500;

4.3: 條件 `非` -- `NOT` 和 `!`

對條件取反

SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE NOT pic_height < 1200;

+----------------------+--------+--------+
| 路徑| 寬/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: 散點匹配 `IN(v1,v2,v3,...)`

符合v1,v2,v3,...之一可匹配

SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height IN (1696,2268); 

+----------------------+--------+--------+
| 路徑| 寬/px| 高/px|
+----------------------+--------+--------+
| ndbMXlwKuCpiiVqC.jpg |1701 |2268 |
| XQWGrglfjGVuJfzJ.jpg |1200 |1696 |
+----------------------+--------+--------+

4.5: 區間匹配 `BETWEEN v1 AND v2`

v1,v2之間可匹配

SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_height BETWEEN 1696 AND 2268; 

+----------------------+--------+--------+
| 路徑| 寬/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：模糊查詢： `LIKE`

'%'匹配任意多個字元,'_'匹配任意單個字元

mysql>
SELECT 
pic_path AS 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_path LIKE 'androi%'; 

+----------------------------------------------+--------+--------+
| 路徑| 寬/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 路徑 , 
pic_width AS '寬/px', 
pic_height AS '高/px' 
FROM pic 
WHERE pic_path LIKE 'p_em%';

+--------------------------------------------+--------+--------+
| 路徑| 寬/px| 高/px|
+--------------------------------------------+--------+--------+
| poem\世界·綻放.jpg|1148 |712 |
| poem\我愛你，是火山岩的緘默.jpg|690 |397 |
| poem\枝·你是樹的狂舞.jpg|500 |333 |
| poem\海與鹿王.jpg|799 |499 |
| poem\遊夢人·詩的誕生.jpg|800 |444 |
| poem\珊瑚墓地.jpg|1104 |719 |
+--------------------------------------------+--------+--------+

4.7:比較符號 `= != < > <= >=`

小學生都知道的，就不廢話了，檢視一下小於10Kb的圖片

mysql>
SELECT 
pic_path AS 路徑 ,
pic_length AS '大小/byte' 
FROM pic 
WHERE pic_length < 10*1024;

+----------------------------------------------+-------------+
| 路徑| 大小/byte|
+----------------------------------------------+-------------+
| 30X20.jpg|10158 |
| android\613f2b8f0eaa8f63bedce9781527c9ab.png |4001 |
| android\94b5c41232f9761403890c09c2b1aae3.png |4001 |
| android\d3fd676f224f0734beb48d0c0d2f4e66.png |4001 |
| udp傳送與接收訊息_控制檯.png|9184 |
+----------------------------------------------+-------------+

5. `GROUP BY` 分組查詢

會先排序，再列出

|--- GROUP BY
SELECT 
pic_mime AS "型別",
avg(pic_length) AS '平均大小/byte' ,
count(pic_length) AS '總數量/個' ,
min(pic_length) AS '最小值/byte' ,
max(pic_length) AS '最大值/byte' ,
sum(pic_length) AS '總和/byte'
FROM pic 
GROUP BY pic_mime;

+--------+-------------------+---------------+----------------+----------------+-------------+
| 型別| 平均大小/byte| 總數量/個| 最小值/byte| 最大值/byte| 總和/byte|
+--------+-------------------+---------------+----------------+----------------+-------------+
|0 |141518.8734 |229 |4001 |829338 |32407822 |
|1 |2133272.8000 |60 |10158 |116342886 |127996368 |
+--------+-------------------+---------------+----------------+----------------+-------------+

6.結果集篩選： `HAVING`

現在查詢寬高比在1.1和1.3之間的圖片

|-- 如果用WHERE 來查詢 感覺有點不優雅
SELECT 
pic_path AS 路徑 , 
pic_width/pic_height AS '寬高比'
FROM pic 
WHERE pic_width/pic_height > 1.1 && pic_width/pic_height<1.3; 

+------------------------------------------------------------------+-----------+
| 路徑| 寬高比|
+------------------------------------------------------------------+-----------+
| dQXbnTRjUdNxhiyl.jpg|1.2308 |
| JsXHWmKqOlziKmeA.jpg|1.2600 |
| logo\android\Android原生繪圖之讓你瞭解View的運動.png|1.2884 |
| 洛天依.jpg|1.1990 |
+------------------------------------------------------------------+-----------+

|-- AS 相當於將列取了變數，對結果集再進行篩選用HAVING,用WHERE則報錯，找不到列
SELECT 
pic_path AS 路徑 , 
pic_width/pic_height AS ratio 
FROM pic 
HAVING ratio > 1.1 && ratio <1.3;

+------------------------------------------------------------------+--------+
| 路徑| ratio|
+------------------------------------------------------------------+--------+
| dQXbnTRjUdNxhiyl.jpg| 1.2308 |
| JsXHWmKqOlziKmeA.jpg| 1.2600 |
| logo\android\Android原生繪圖之讓你瞭解View的運動.png| 1.2884 |
| 洛天依.jpg| 1.1990 |
+------------------------------------------------------------------+--------+

7.結果排序： `ORDER BY`

按照ratio將序排列

SELECT 
pic_path AS 路徑 , 
pic_width/pic_height AS ratio 
FROM pic 
HAVING ratio > 1.1 && ratio <1.3;
ORDER BY ratio DESC 

+------------------------------------------------------------------+--------+
| 路徑| ratio|
+------------------------------------------------------------------+--------+
| dQXbnTRjUdNxhiyl.jpg| 1.2308 |
| JsXHWmKqOlziKmeA.jpg| 1.2600 |
| logo\android\Android原生繪圖之讓你瞭解View的運動.png| 1.2884 |
| 洛天依.jpg| 1.1990 |
+------------------------------------------------------------------+--------+

8.控制條目數： `LIMIT`

|-- 偏移一條，取兩條
SELECT 
pic_path AS 路徑 , 
pic_width/pic_height AS ratio 
FROM pic 
HAVING ratio > 1.1 && ratio <1.3
ORDER BY ratio DESC LIMIT 1,2;

+----------------------+--------+
| 路徑| ratio|
+----------------------+--------+
| JsXHWmKqOlziKmeA.jpg | 1.2600 |
| dQXbnTRjUdNxhiyl.jpg | 1.2308 |
+----------------------+--------+

三、子查詢 `(LEVER 3)`

1.查詢大於平均尺寸的圖片 -- `WHERE`

|--- 出現在其他SQL語句內的SELECT語句
|--- 子查詢必須在()內
|--- 增刪改查都可以進行子查詢,返回：標量，行，列或子查詢

|-- 1-1：查出圖片平均大小
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 篩選
SELECT 
pic_path AS 路徑 , 
pic_lengthAS '大小/byte' 
FROM pic 
WHERE pic_length > 555031.80;

+----------------------------------------------+-------------+
| 路徑| 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 |
+----------------------------------------------+-------------+

|--- 也就是將一個語句包在WHERE 條件裡
SELECT 
pic_path AS 路徑 , 
pic_lengthAS '大小/byte' 
FROM pic 
WHERE pic_length > (
SELECT 
ROUND(AVG(pic_length),2) 
FROM pic
);

2.查出每種型別的最新插入的圖片 -- `WHERE`

SELECT 
pic_path AS 路徑 , 
pic_mime AS 型別 
FROM pic 
WHERE id IN (
SELECT 
max(id)
FROM pic 
GROUP BY pic_mime
);

+------------------+--------+
| 路徑| 型別|
+------------------+--------+
| 洛天依.jpg|1 |
| 虛擬機器棧.png|0 |
+------------------+--------+

3.FROM子查詢 -- `FROM`

SELECT 
id, 
pic_path AS 路徑 , 
pic_lengthAS '大小/byte' 
FROM pic 
WHERE id>=10&&id<=15 
ORDER BY pic_length DESC;

+----+----------------------------------------------+-------------+
| id | 路徑| 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 |
+----+----------------------------------------------+-------------+

|--- 將查詢結果當做一張表，再查詢操作
SELECT 
id,路徑 FROM (
SELECT 
id, 
pic_path AS 路徑 , 
pic_lengthAS '大小/byte' 
FROM pic 
WHERE id>=10&&id<=15 
ORDER BY pic_length DESC
) AS result 
WHERE `大小/byte` < 59999;

+----+----------------------------------------------+
| id | 路徑|
+----+----------------------------------------------+
| 10 | android\0655e07d6717847489cd222c9c9e0b1d.png |
| 12 | android\07a4dc9b4b207cb420a71cbf941ad45a.png |
| 13 | android\07abb7972a5638b53afa3b5eb98b19c1.png |
+----+----------------------------------------------+

四、連線查詢

0.建立關聯表

首先連線查詢要多張表，現在建一個 mime_type 的表

|--- 建表
CREATE TABLE mime_type(
mime_id SMALLINT UNSIGNED PRIMARY KEY,
mime_info CHAR(24)
 );

|--- 插入資料
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|
+---------+---------------+

|-- 為了說明問題，pic表新增一條測試資料：pic_mime = 8也就是 mime_type表找不到時
INSERT INTO pic(pic_path,pic_length,pic_mime,pic_width,pic_height) VALUES('test.jpg',100,8,300,200);

1.內連線查詢 `INNER JOIN`

SELECT 待查屬性 FROM 表1 INNER JOIN 表2 ON 條件 WHERE 條件

SELECT id, pic_path AS 路徑 , mime_type.mime_info AS 型別 , pic_length 
FROM pic INNER JOIN mime_type 
ON pic.pic_mime = mime_type.mime_id 
ORDER BY id DESC LIMIT 4;

+-----+------------------+------------+------------+
| id| 路徑| 型別| pic_length |
+-----+------------------+------------+------------+
| 289 | 虛擬機器棧.png| image/png|63723 |
| 288 | 統一返回.png| image/png|29485 |
| 287 | 洛天依.jpg| image/jpeg |42117 |
| 286 | 標記整理.png| image/png|29288 |
+-----+------------------+------------+------------+

2.左連線查詢 : `LEFT JOIN`

保持左表的記錄完整性，右表查不到就擺 NULL

SELECT id, pic_path AS 路徑 , mime_type.mime_info AS 型別 , pic_length 
FROM pic LEFT JOIN mime_type 
ON pic.pic_mime = mime_type.mime_id 
ORDER BY id DESC LIMIT 4;

+-----+------------------+------------+------------+
| id| 路徑| 型別| pic_length |
+-----+------------------+------------+------------+
| 290 | test.jpg| NULL|100 |
| 289 | 虛擬機器棧.png| image/png|63723 |
| 288 | 統一返回.png| image/png|29485 |
| 287 | 洛天依.jpg| image/jpeg |42117 |
+-----+------------------+------------+------------+

3. 右(外)連線查詢 : `RIGHT JOIN`

保持右表的記錄完整性，左表查不到就擺 NULL

SELECT id, pic_path AS 路徑 , mime_type.mime_info AS 型別 , pic_length 
FROM pic RIGHT JOIN mime_type 
ON pic.pic_mime = mime_type.mime_id 
ORDER BY id LIMIT 8;

+------+--------------------------------------+---------------+------------+
| id| 路徑| 型別| 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)連線 (偽): `使用UNION`

MySQL不支援全外連線，所以只能採取關鍵字UNION來聯合左、右連線的方法

UNION : 將若干條sql的查詢結果集合併成一個。 UNION ALL 不會覆蓋相同結果

SELECT id, pic_path AS 路徑 , mime_type.mime_info AS 型別 , pic_length 
FROM pic LEFT JOIN mime_type ON pic.pic_mime = mime_type.mime_id 
UNION(
SELECT id, pic_path AS 路徑 , mime_type.mime_info AS 型別 , pic_length 
FROM pic RIGHT JOIN mime_type ON pic.pic_mime = mime_type.mime_id 
) 
ORDER BY id DESC;

+------+------------------------------------------------------------------------------------+---------------+------------+
| id| 路徑| 型別| pic_length |
+------+------------------------------------------------------------------------------------+---------------+------------+
|290 | test.jpg| NULL|100 |
|289 | 虛擬機器棧.png| image/png|63723 |
|288 | 統一返回.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小測試

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 建庫/表

1、關於操作資料庫

SHOW DATABASES; # 顯示所有的資料庫
SHOW CREATE DATABASE <資料庫名> # 檢視資料庫建立資訊
USE <資料庫名>; # 使用資料庫
CREATE DATABASE <資料庫名> [CHARACTER SET <字符集>]; # 建立一個將的資料庫指定字符集
ALTER DATABASE <資料庫名> CHARACTER SET <字符集>; # 修改資料庫字符集
DROP DATABASE<資料庫名>; # 傳說中的刪庫跑路
SELECT DATABASE(); # 檢視當前選中的資料庫

2.顯示資料庫資訊

SHOW TABLES; # 展示當前資料庫中的表
SHOW TABLES FROM mysql # 展示指定資料庫中的表
DESC <表名>; # 查看錶結構
SHOW COLUMNS FROM <表名>; # 查看錶結構

3.建立表

|-- UNSIGNED 無符號AUTO_INCREMENT 自增長 
|-- ZEROFILL 前面自動填 0 , 預設 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 (); #預設值測試
 mysql> SELECT * FROM create_test;
+----+-------+
| id | code|
+----+-------+
|1 | 00005 |
|2 | 00000 |
+----+-------+

4.為表增加屬性

ALTER TABLE <表名> ADD 屬性資訊 [AFTER 屬性] ;

|-- 看一下當前表結構

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可將屬性排在指定屬性之後(強迫症專用)
|-- 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||
+----------+------------------------------+------+-----+---------+----------------+

|-- 一次新增多個屬性
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.為表刪除屬性

ALTER TABLE <表名> DROP 屬性

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.修改屬性的型別

ALTER TABLE <表名> MODIFY 屬性屬性型別 [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||
+----------+------------------------------+------+-----+---------+----------------+

|-- 將某個屬性移到最頂
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.修改表的屬性名

ALTER TABLE <表名> CHANGE 原屬性新屬性新屬性型別;

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 舊錶名 RENAME 新表名;
方式二： RENAME TABLE 舊錶名 TO 新表名;

ALTER TABLE create_test RENAME 阿姆斯特朗迴旋加速噴氣式阿姆斯特朗炮;
mysql> SHOW TABLES;
+--------------------------------------------------------+
| Tables_in_datatype|
+--------------------------------------------------------+
| 阿姆斯特朗迴旋加速噴氣式阿姆斯特朗炮|
| a|
| b|
| mime_type|
| pic|
| type_number|
+--------------------------------------------------------+

RENAME TABLE 阿姆斯特朗迴旋加速噴氣式阿姆斯特朗炮 TO toly;

mysql> SHOW TABLES;
+--------------------+
| Tables_in_datatype |
+--------------------+
| a|
| b|
| mime_type|
| pic|
| toly|
| type_number|
+--------------------+

SQL 的基礎就這樣 , 下篇見

MySQL指南之SQL語句基礎

零、結構化查詢語言：SQL(Structured Query Language)

準備活動：建立庫和表

一、DML 資料庫記錄操作 LEVEL 1

1、記錄的插入操作

2、記錄的更新操作

3.記錄的刪除操作

4.記錄的查詢操作

二、圖片表pic (LEVER 2)

1.建表語句

2.查詢操作 AS 的作用

3.查詢是屬性可參與運算

4. WHERE 條件的千變萬化

4.1: 條件 與 -- AND 和 &&

4.2: 條件 或 -- OR 和 ||

4.3: 條件 非 -- NOT 和 !

4.4: 散點匹配 IN(v1,v2,v3,...)

4.5: 區間匹配 BETWEEN v1 AND v2

4.6：模糊查詢： LIKE

4.7:比較符號 = != < > <= >=

5. GROUP BY 分組查詢

6.結果集篩選： HAVING

7.結果排序： ORDER BY

8.控制條目數： LIMIT

三、子查詢 (LEVER 3)

1.查詢大於平均尺寸的圖片 -- WHERE

2.查出每種型別的最新插入的圖片 -- WHERE

3.FROM子查詢 -- FROM