Sql学习拾遗（一）

     告别2013，进入崭新的2014，自己决定将数据库作为自己新的一年的工作学习的开始。工作中不可避免地要和数据库打交道，自己之前参加青鸟培训的时候曾经接触过微软的VS中自带的SqlServer2005，那个时候也简单地写过一些C#的数据库程序，但是之后没有继续使用，因而很快就都忘记了。所以现在需要重新来复习一下，为下一步的工作做好准备。今天先来从基本的sql语句开始吧，不针对特定平台，也不会详细地列出语句用法，主要针对自己之前遗忘或者没有接触掌握的内容做些梳理。

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一、构建测试用数据库
     这里自己学习的材料是经典教材《Sql必知必会》，对于自己熟悉常用的sql命令足够了，计划用两到三天的时间来完成这个部分的学习。为了随时验证所学的东西，这里采用书中提供的数据库作为测试用例。官方提供的是mdb格式的文件，默认应当使用Access来打开，但是自己安装了Ubuntu的虚拟环境，配置了MySql，因此决定利用脚本在MySql中搭建数据库，方法比较简单，执行创建初始化脚本即可：
Create脚本：

--------------------------------------------
-- Sams Teach Yourself SQL in 10 Minutes
--
-- Example table creation scripts for MySQL.
--------------------------------------------


-------------------------
-- Create Customers table
-------------------------
CREATE TABLE Customers
(
  cust_id char(10) NOT NULL ,
  cust_name char(50) NOT NULL ,
  cust_address char(50) NULL ,
  cust_city char(50) NULL ,
  cust_state char(5) NULL ,
  cust_zip char(10) NULL ,
  cust_country char(50) NULL ,
  cust_contact char(50) NULL ,
  cust_email char(255) NULL
);

--------------------------
-- Create OrderItems table
--------------------------
CREATE TABLE OrderItems
(
  order_num  int NOT NULL ,
  order_item int NOT NULL ,
  prod_id char(10) NOT NULL ,
  quantity   int NOT NULL ,
  item_price decimal(8,2) NOT NULL
);


----------------------
-- Create Orders table
----------------------
CREATE TABLE Orders
(
  order_num  int NOT NULL ,
  order_date datetime NOT NULL ,
  cust_id char(10) NOT NULL
);

------------------------
-- Create Products table
------------------------
CREATE TABLE Products
(
  prod_id char(10) NOT NULL ,
  vend_id char(10) NOT NULL ,
  prod_name char(255) NOT NULL ,
  prod_price decimal(8,2) NOT NULL ,
  prod_desc  text NULL
);

-----------------------
-- Create Vendors table
-----------------------
CREATE TABLE Vendors
(
  vend_id char(10) NOT NULL ,
  vend_name char(50) NOT NULL ,
  vend_address char(50) NULL ,
  vend_city char(50) NULL ,
  vend_state char(5) NULL ,
  vend_zip char(10) NULL ,
  vend_country char(50) NULL
);


----------------------
-- Define primary keys
----------------------
ALTER TABLE Customers ADD PRIMARY KEY (cust_id);
ALTER TABLE OrderItems ADD PRIMARY KEY (order_num, order_item);
ALTER TABLE Orders ADD PRIMARY KEY (order_num);
ALTER TABLE Products ADD PRIMARY KEY (prod_id);
ALTER TABLE Vendors ADD PRIMARY KEY (vend_id);


----------------------
-- Define foreign keys
----------------------
ALTER TABLE OrderItems ADD CONSTRAINT FK_OrderItems_Orders FOREIGN KEY (order_num) REFERENCES Orders (order_num);
ALTER TABLE OrderItems ADD CONSTRAINT FK_OrderItems_Products FOREIGN KEY (prod_id) REFERENCES Products (prod_id);
ALTER TABLE Orders ADD CONSTRAINT FK_Orders_Customers FOREIGN KEY (cust_id) REFERENCES Customers (cust_id);
ALTER TABLE Products ADD CONSTRAINT FK_Products_Vendors FOREIGN KEY (vend_id) REFERENCES Vendors (vend_id);

之后配置Populate脚本：

----------------------------------------------
-- Sams Teach Yourself SQL in 10 Minutes
--
-- Example table population scripts for MySQL.
----------------------------------------------


---------------------------
-- Populate Customers table
---------------------------
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES('1000000001', 'Village Toys', '200 Maple Lane', 'Detroit', 'MI', '44444', 'USA', 'John Smith', '[e-mail]');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact)
VALUES('1000000002', 'Kids Place', '333 South Lake Drive', 'Columbus', 'OH', '43333', 'USA', 'Michelle Green');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES('1000000003', 'Fun4All', '1 Sunny Place', 'Muncie', 'IN', '42222', 'USA', 'Jim Jones', '[e-mail]');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact, cust_email)
VALUES('1000000004', 'Fun4All', '829 Riverside Drive', 'Phoenix', 'AZ', '88888', 'USA', 'Denise L. Stephens', '[e-mail]');
INSERT INTO Customers(cust_id, cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country, cust_contact)
VALUES('1000000005', 'The Toy Store', '4545 53rd Street', 'Chicago', 'IL', '54545', 'USA', 'Kim Howard');

-------------------------
-- Populate Vendors table
-------------------------
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('BRS01','Bears R Us','123 Main Street','Bear Town','MI','44444', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('BRE02','Bear Emporium','500 Park Street','Anytown','OH','44333', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('DLL01','Doll House Inc.','555 High Street','Dollsville','CA','99999', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('FRB01','Furball Inc.','1000 5th Avenue','New York','NY','11111', 'USA');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('FNG01','Fun and Games','42 Galaxy Road','London', NULL,'N16 6PS', 'England');
INSERT INTO Vendors(vend_id, vend_name, vend_address, vend_city, vend_state, vend_zip, vend_country)
VALUES('JTS01','Jouets et ours','1 Rue Amusement','Paris', NULL,'45678', 'France');

--------------------------
-- Populate Products table
--------------------------
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BR01', 'BRS01', '8 inch teddy bear', 5.99, '8 inch teddy bear, comes with cap and jacket');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BR02', 'BRS01', '12 inch teddy bear', 8.99, '12 inch teddy bear, comes with cap and jacket');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BR03', 'BRS01', '18 inch teddy bear', 11.99, '18 inch teddy bear, comes with cap and jacket');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BNBG01', 'DLL01', 'Fish bean bag toy', 3.49, 'Fish bean bag toy, complete with bean bag worms with which to feed it');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BNBG02', 'DLL01', 'Bird bean bag toy', 3.49, 'Bird bean bag toy, eggs are not included');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('BNBG03', 'DLL01', 'Rabbit bean bag toy', 3.49, 'Rabbit bean bag toy, comes with bean bag carrots');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('RGAN01', 'DLL01', 'Raggedy Ann', 4.99, '18 inch Raggedy Ann doll');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('RYL01', 'FNG01', 'King doll', 9.49, '12 inch king doll with royal garments and crown');
INSERT INTO Products(prod_id, vend_id, prod_name, prod_price, prod_desc)
VALUES('RYL02', 'FNG01', 'Queen doll', 9.49, '12 inch queen doll with royal garments and crown');

------------------------
-- Populate Orders table
------------------------
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20005, '2004-05-01', '1000000001');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20006, '2004-01-12', '1000000003');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20007, '2004-01-30', '1000000004');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20008, '2004-02-03', '1000000005');
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20009, '2004-02-08', '1000000001');

----------------------------
-- Populate OrderItems table
----------------------------
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20005, 1, 'BR01', 100, 5.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20005, 2, 'BR03', 100, 10.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20006, 1, 'BR01', 20, 5.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20006, 2, 'BR02', 10, 8.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20006, 3, 'BR03', 10, 11.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 1, 'BR03', 50, 11.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 2, 'BNBG01', 100, 2.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 3, 'BNBG02', 100, 2.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 4, 'BNBG03', 100, 2.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20007, 5, 'RGAN01', 50, 4.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 1, 'RGAN01', 5, 4.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 2, 'BR03', 5, 11.99);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 3, 'BNBG01', 10, 3.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 4, 'BNBG02', 10, 3.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20008, 5, 'BNBG03', 10, 3.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20009, 1, 'BNBG01', 250, 2.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20009, 2, 'BNBG02', 250, 2.49);
INSERT INTO OrderItems(order_num, order_item, prod_id, quantity, item_price)
VALUES(20009, 3, 'BNBG03', 250, 2.49);

      完成之后我们可以进入到mysql中去查看已经创建好的数据库和表：
     mysql -u username -p > password;
     show databases;
     use database_name;       //这里创建了example数据库作为测试
     show tables;
     desc(ribe) table_name;    //此命令可以查看表结构，如各列的名称和类型等

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二、基本的select语句
     在继续介绍基本语句之前，先来列出自己感觉重要的几个要点：
1. DBMS会管理着多个数据库，每个数据库由表组成，表由一条一条的记录构成，每条记录则是不同数据类型的集合；
2. 每个表中都有一个主键，用于唯一标识每条记录，因此要求主键列具有以下属性：
   -‘1-1’对应：每条记录都有一个唯一主键，不同的记录主键不同；
   -   不能使用update命令对记录的主键更新修改；
   -   可以delete记录，但是删掉的记录的主键永远不可在表中复用，即新纪录不能使用用过的主键，不管该主键对应的记录是否还存在；
3. 书写规则：
   -   Sql语句不区分大小写，因此select和SELECT效果是一样的，一般为了便于阅读，建议关键词（如SELECT/UPDATE等）大写，其余小写；
   -   Sql语句不区分空格，因此column = 1与column=1是相同的；
   -   Sql语句一般要求使用';'作为每条语句的结束，有些DBMS可能不要求，但是为了统一考虑，一般建议都使用';'作为命令结束；
4. 排序语句：
   -   Order by一般放置在SELECT语句的末尾，对于已经进行过各种条件过滤之后的语句再排序；
   -   Order by默认是升序排列，即数字大小或字母表顺序，可以使用DESC指定为降序，仅仅对向前修饰的最近Order by有效；
   -   Order by可以同时使用多列排序，依次排序，如Order by A, B,C 则先按A排序，A相同的再按B排序，依次类推；
5. 条件过滤-WHERE：
   -   WHERE使用时，如果与字符串关键词比较，必须使用''标识字符串；数字关键字不需要，''仅仅用来表示字符串；
   -   Between A and B范围语句包含起点和终点A和B；
   -   IS NULL用来筛选列值为空的记录；
   -   WHERE column IN (SET);
【基本的语句结构：SELECT   查什么：列名1，列名2，列名...   FROM   从哪查：table_name   WHERE IS NULL/NOT 条件   ORDER BY 指标列集合 DESC】