下列代碼是我在學習MOOC的視頻時做的一些練習，內容比較簡單，主要涉及子查詢與連接，大家可以作為練習參考直接使用(更多相關代碼可以訪問 我的GITHUB

代碼如下：

Create database MOOC;Use MOOC; SET NAMES utf8;CREATE TABLE IF NOT EXISTS tdb_goods(goods_id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,goods_name VARCHAR(150) NOT NULL,goods_cate VARCHAR(40) NOT NULL,brand_name VARCHAR(40) NOT NULL,goods_price DECIMAL(15,3) UNSIGNED NOT NULL DEFAULT 0,is_show BOOLEAN NOT NULL DEFAULT 1,is_saleoff BOOLEAN NOT NULL DEFAULT 0);

ALTER TABLES tdb_goods CHARACTER SET utf8;Delete from tdb_goods; //測試安全模式INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('R510VC 15.6英寸筆記本','筆記本','華碩','3399',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('Y400N 14.0英寸筆記本電腦','筆記本','聯想','4899',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('G150TH 15.6英寸游戲本','游戲本','雷神','8499',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('X550CC 15.6英寸筆記本','筆記本','華碩','2799',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('X240(20ALA0EYCD) 12.5英寸超極本','超級本','聯想','4999',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('U330P 13.3英寸超極本','超級本','聯想','4299',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('SVP13226SCB 13.3英寸觸控超極本','超級本','索尼','7999',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('iPad mini MD531CH/A 7.9英寸平板電腦','平板電腦','蘋果','1998',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('iPad Air MD788CH/A 9.7英寸平板電腦 （16G WiFi版）','平板電腦','蘋果','3388',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(' iPad mini ME279CH/A 配備 Retina 顯示屏 7.9英寸平板電腦 （16G WiFi版）','平板電腦','蘋果','2788',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('IdeaCentre C340 20英寸一體電腦 ','臺式機','聯想','3499',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('Vostro 3800-R1206 臺式電腦','臺式機','戴爾','2899',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('iMac ME086CH/A 21.5英寸一體電腦','臺式機','蘋果','9188',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('AT7-7414LP 臺式電腦 （i5-3450四核 4G 500G 2G獨顯 DVD 鍵鼠 Linux ）','臺式機','宏碁','3699',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('Z220SFF F4F06PA工作站','服務器/工作站','惠普','4288',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('PowerEdge T110 II服務器','服務器/工作站','戴爾','5388',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('Mac Pro MD878CH/A 專業級臺式電腦','服務器/工作站','蘋果','28888',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(' HMZ-T3W 頭戴顯示設備','筆記本配件','索尼','6999',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('商務雙肩背包','筆記本配件','索尼','99',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('X3250 M4機架式服務器 2583i14','服務器/工作站','IBM','6888',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('玄龍精英版 筆記本散熱器','筆記本配件','九州風神',default,DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES(' HMZ-T3W 頭戴顯示設備','筆記本配件','索尼','6999',DEFAULT,DEFAULT);INSERT tdb_goods (goods_name,goods_cate,brand_name,goods_price,is_show,is_saleoff) VALUES('商務雙肩背包','筆記本配件','索尼','99',DEFAULT,DEFAULT);Select count(goods_id) as How_many from tdb_goods;Select * from tdb_goods\G/****************子查詢練習****************///查詢價格大于平均價格的產品 select ROUND(AVG(goods_price),1) as Avgerage_price from tdb_goods; 寫法一 select goods_id, goods_name, goods_price from tdb_goods group by goods_price, goods_id /*GROUP BY可以放置任意字段作為函數依據*/havinggoods_price >= ROUND(AVG(goods_price),1);

寫法二 select goods_id, goods_name, goods_price from tdb_goods where goods_price >= (selectROUND(AVG(goods_price),1) from tdb_goods); //查詢價格大于超極本的筆記本 select goods_id, goods_name, goods_price from tdb_goods where goods_price >= any (selectgoods_price from tdb_goods where goods_cate = '超級本'); select * from mysql.user; show variables like 'autocommit';use mooc; select * from tdb_goods;**STEP 1** //創建新的數據表作為外鍵INSERT 子查詢插入 //用于第二步的模式分解（多表更新）Create table if not exists tb_cates( cate_id smallint unsigned not null auto_increment, cate_name varchar(20) not null, primary key(cate_id) );Select goods_cate From tdb_goods group by goods_cate; DESC tdb_goods; /*根據每一列的數據類型插入，即目標列和查詢列必須一致*/**STEP 2** Insert INTO tb_cates(cate_name) /*和select嵌套查詢不同，insert不需要=(select)*/Select goods_cate From tdb_goods group by goods_cate; Select * from tb_cates group by cate_id ASC;//通過TB-cates中對應的序號將原表類別使用ID替代，即連接Update tdb_goods INNER join tb_cates ON tdb_goods.goods_cate = tb_cates.cate_nameSET tdb_goods.goods_cate = tb_cates.cate_idwhere tdb_goods.goods_id >= 1; /*安全模式下必須要WHERE+KEY進行UPDATE*/**STEP 3** //將STEP 1 & 2合并為一句SELECT brand_name, count(brand_name)from tdb_goods GROUP BY goods_cate ASC;Create Table goods_brands( brand_id smallint unsigned auto_increment, brand_name VARCHAR(40) default null, primary key(brand_id) ) Select brand_id from tdb_goods group by brand_id;SELECT * FROM goods_brands;UPDATE tdb_goods as A INNER JOIN goods_brands AS bON /*使用join形成的外鍵稱為“事實外鍵”，不需要FK聲明*/A.brand_name = B.brand_nameSET A.brand_name = B.brand_id;//測試：修改原表數據類型Alter table tdb_goods Change goods_cate cate_id smallint unsigned not null, Change brand_name brand_id smallint unsigned not null ;ALTER TABLE tb_cates rename to goods_cate;

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