图解SQL子查询实例

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1 创建示例表

先创建示例表；

--------------------------- 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  varchar(1000) 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 WITH NOCHECK ADD CONSTRAINT PK_Customers PRIMARY KEY CLUSTERED (cust_id);ALTER TABLE OrderItems WITH NOCHECK ADD CONSTRAINT PK_OrderItems PRIMARY KEY CLUSTERED (order_num, order_item);ALTER TABLE Orders WITH NOCHECK ADD CONSTRAINT PK_Orders PRIMARY KEY CLUSTERED (order_num);ALTER TABLE Products WITH NOCHECK ADD CONSTRAINT PK_Products PRIMARY KEY CLUSTERED (prod_id);ALTER TABLE Vendors WITH NOCHECK ADD CONSTRAINT PK_Vendors PRIMARY KEY CLUSTERED (vend_id);------------------------ Define foreign keys----------------------ALTER TABLE OrderItems ADDCONSTRAINT FK_OrderItems_Orders FOREIGN KEY (order_num) REFERENCES Orders (order_num),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 ADDCONSTRAINT FK_Products_Vendors FOREIGN KEY (vend_id) REFERENCES Vendors (vend_id);

----------------------------- 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', 'sales@villagetoys.com');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', 'jjones@fun4all.com');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', 'dstephens@fun4all.com');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, '2012-05-01', '1000000001');INSERT INTO Orders(order_num, order_date, cust_id)VALUES(20006, '2012-01-12', '1000000003');INSERT INTO Orders(order_num, order_date, cust_id)VALUES(20007, '2012-01-30', '1000000004');INSERT INTO Orders(order_num, order_date, cust_id)VALUES(20008, '2012-02-03', '1000000005');INSERT INTO Orders(order_num, order_date, cust_id)VALUES(20009, '2012-02-08', '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);

示例表的创建和插入数据脚本可从此页底部下载；

http://www.forta.com/books/0672336073/

以下是Customers和Orders表的情况；

2 独立单值子查询（独立标量子查询）

子查询返回的是单个值，而不是数据集

select *   from customers as C  where C.cust_id=(  select O.cust_id from Orders as O where O.order_num = 20008 );

注：使用单值独立子查询时，一定要保证子查询返回的是单个值，而不是数据集；
若返回的是数据集，则会出现如下状况：

3 独立多值子查询

子查询返回的是数据集

select *  from customers as C where C.cust_id IN(  select O.cust_id from Orders as O where O.order_num between 20005 and 20007 );

4 相关子查询

相关子查询最基本的执行逻辑是：将外部表中的 “每一行” 逐行代入到子查询中（理解相关子查询的关键）

select *   from Customers as C  where exists (     select * from  Orders as O     where O.cust_id=C.cust_id and (O.order_num between 20005 and 20008) );

5 作为计算字段使用子查询

统计顾客名字，顾客所在的州，顾客的订单数；

select cust_name,cust_state,(select COUNT(*) from Orders where Orders.cust_id=Customers.cust_id) as Ordersfrom Customersorder by cust_name;

第三列是子查询，统计每个顾客的订单数；

第三列的子查询单独执行情况如下；

select COUNT(*) from Orders where cust_id='1000000001';

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