数据库SQL语句学习笔记-检索数据库
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首先设置好此连载笔记的演示所用的表
CREATE database sells; #创建名叫sells的数据库 USE sells; #告诉mysql，我要开始使用这个数据库了 CREATE TABLE Customers #创建Customers表 ( 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 TABLE OrderItems #创建OrderItems表 ( 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 TABLE Orders #创建Orders表 ( order_num int NOT NULL , order_date datetime NOT NULL , cust_id char(10) NOT NULL ); CREATE TABLE Products #创建表Product ( 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 TABLE Vendors #创建表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 ); #设置主键 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); #设置外键 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); #插入记录 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\'); 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\'); 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\'); 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\'); 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);
1. SELECT语句
关键字（keyword）作为SQL组成部分的保留字，不可以作为表或者列的名字。
使用SELECT语句，要清楚需要选择什么？从哪里选择的问题。
2. 检索单个列
SELECT prod_name FROM Products;
结果：
分析：从Product表中检索一个名为prod_name的列。列名写在关键字SELECT之后，FROM关键字表明从哪个表中检索。这样返回的数据没有特定的顺序。
提示：（1）多条SQL语句必须以；分隔
（2）SQL语句不区分大小写，约定俗成的是关键字大写，表名和列名小写
（3）以分号结尾，看到分号就知道这一条语句结束了
3.检索多个列
SELECT关键字后给出多个列名，列名之间以逗号分隔，最后一个列名后不可以加逗号
SELECT prod_id,prod_name,prod_price FROM Products;
结果： 
4.检索所有列
通配符星号（*）可以检索所有列
SELECT * FROM Products;
5. 检索不同的值
SELESTC语句返回所有匹配的行，但是有很多值重复出现，此时就要用到检索不同的值
SELECT DISTINCT vend_id FROM Products;
注意：DISTINCT关键字作用于所有选择的列
6.限制结果
SELECT prod_name FROM Products LIMIT 5;
结果：
LIMIT 5指示MYSQL返回不超过5行数据
LIMIT 5 OFFSET 5从第5行起，检索5个数,注意第一行是0
简写为LIMIT 5,5 第一个数是OFFSET,第二个是LIMIT
7.使用注释
--嵌在行内
# 行内注释，在一行开始处使用#，这一整行都将作为注释
/* */开始结束中间都作为注释
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