SQL语言入门学习，这一篇就够了

1、## SQL 数据操作语言 (DML)
SQL (结构化查询语言)是用于执行查询的语法。但是 SQL 语言也包含用于更新、插入和删除记录的语法。
这些查询和更新语句都来自 SQL 的 DML 部分：

SELECT - 从数据库表中获取数据
UPDATE - 更新数据库表中的数据
DELETE - 从数据库表中删除数据
INSERT INTO - 向数据库表中插入数据

2、## SQL 数据定义语言 (DDL)
SQL 的数据定义语言部分使我们有能力创建或删除表格。我们也可以定义索引（键），规定表之间的链接，以及施加表间的约束。
SQL 中最重要的 DDL 语句:
CREATE TABLE - 创建新表
ALTER TABLE - 变更（改变）数据库表
DROP TABLE - 删除表
CREATE INDEX - 创建索引（搜索键）
DROP INDEX - 删除索引

3、## 下面从DML到DDL分别举例各场景的SQL语言应用
以下数据操作使用样例数据来源SQL语言学习样例数据

------------------------------------------------------数据库查询部分--------------------------------------------------------------

–检索单列、多列、所有列
select prod_name from Products;

select prod_id,prod_name,prod_price
from products;

select * from Products;

–检索不同的值
select vend_id from products;

select distinct vend_id
from products;

select distinct vend_id,prod_price
from products; /不能部分使用distinct/

–限制结果
select top 5 prod_name from products; --不同DBMS语句不同

–使用注释
/select prod_id,prod_name,prod_price
from products;/
select prod_name from Products;

–子句（排序数据）
select prod_name
from Products
order by prod_name; --order by 是select语句中最后一条子句

–按多个列排序
select prod_id,prod_price ,prod_name
from products
order by prod_price ,prod_name;

–按列位置排序
select prod_id,prod_price ,prod_name
from products
order by 2,3;

–指定排序方向
select prod_id,prod_price ,prod_name
from products
order by prod_price desc;

select prod_id,prod_price ,prod_name
from products
order by prod_price desc,prod_name;

–where 子句的使用
select prod_name,prod_price
from products
where prod_price=3.49;

select prod_name,prod_price
from products
where prod_price<10;

–不匹配检查
select vend_id,prod_name
from products
where vend_id <>‘DLL01’;

select vend_id,prod_name
from products
where vend_id !=‘DLL01’;

–范围值检查
select prod_name,prod_price
from products
where prod_price between 5 and 10;

–空值检查
select prod_name
from products
where prod_price is null;

select cust_name
from Customers
where cust_email is null;

–and 操作符
select prod_id,prod_name,prod_price
from products
where vend_id=‘DLL01’ and prod_price <=4;

–or 操作符
select prod_name,prod_price
from products
where vend_id=‘DLL01’ or vend_id=‘BRS01’;

–求值顺序(列出价格为10美元及以上,且由DLL01或BRS01制造的所有产品)
select prod_name,prod_price
from products
where prod_price >=10 and (vend_id=‘DLL01’ or vend_id=‘BRS01’);

select vend_id,prod_name,prod_price
from products
where vend_id=‘DLL01’ or vend_id=‘BRS01’ and prod_price >=10 ; --and优先级比or高

–in操作符
select vend_id,prod_name,prod_price
from products
where vend_id in (‘DLL01’,‘BRS01’); --功能与or相当，且比一组or操作符执行更快

–not操作符
select prod_name
from products
where not vend_id =‘DLL01’; --此处功能与<>相同，与其他操作符组合使用，否定其后跟着的条件

–like操作符、"%"通配符
select prod_id,prod_name
from Products
where prod_name like ‘Fish%’;

select prod_id,prod_name
from Products
where prod_name like ‘%bean bag%’;

select prod_id,prod_name
from Products
where prod_name like ‘F%y’; --"%"不能匹配null

–"“通配符
select prod_id,prod_name
from Products
where prod_name like ‘__ inch teddy bear’; --”"只能匹配一个字符

–"[]"通配符–指定字符集
select cust_contact
from Customers
where cust_contact like ‘[JM]%’
order by cust_contact;

select cust_contact
from Customers
where cust_contact like ‘[^JM]%’
order by cust_contact; --前缀字符^否定

select cust_contact
from Customers
where not cust_contact like ‘[JM]%’
order by cust_contact;

–拼接字段
select vend_name+’(’+vend_country+’)’
from Vendors
order by vend_name;

select rtrim(vend_name)+’(’+rtrim(vend_country)+’)’
from Vendors
order by vend_name; --去掉右边空格,trim(),rtrim()右,ltrim()左

–使用别名
select rtrim(vend_name)+’(’+rtrim(vend_country)+’)’
as vend_title
from Vendors
order by vend_name;

–执行算数计算
select prod_id,quantity,item_price
from OrderItems
where order_num =20008;

select prod_id,
quantity,
item_price,
quantity*item_price as expanded_price
from OrderItems
where order_num =20008;

–文本处理函数
select vend_name,UPPER(vend_name) as vend_name_upcase
from Vendors
order by vend_name; --转换为大写

–soundex()函数：发音比较
select cust_name,cust_contact
from Customers
where cust_contact = ‘Micheal Green’;

select cust_name,cust_contact
from Customers
where soundex(cust_contact) = soundex(‘Micheal Green’);

–日期和时间处理函数
select order_num
from Orders
where DATEPART(YY,order_date)=2012;

/Oracle中实现
select order_num
from Orders
where to_number(to_char(order_date,‘yyyy’))=2012;/

select order_num,order_date
from Orders
where order_date between CONVERT(VARCHAR(23),‘2012-02-01’,121)
and convert(VARCHAR(23),‘12-31-2012’,121) ; --convert函数把日期转换为新数据类型的通用函数

–avg()函数:忽略值为null的行
select AVG(prod_price) as avg_prce
from Products;

select AVG(prod_price) as avg_prce
from Products
where vend_id=‘DLL01’;

–count()函数:count()包含空值(null)的所有行数；count(column)特定列有值的行计数，忽略null值
select COUNT() as num_cust
from Customers;

select COUNT(cust_email) as num_cust
from Customers;

–max()、min()函数：可用于数据、日期、文本，用于文本是，返回按该列排序后的最后一行(最前面一行)
select MAX(prod_price) as max_price
from Products;

select MIN(prod_price) as min_price
from Products;

–sum()函数:忽略值为null的行
select sum(quantity) as items_ordered
from orderitems
where order_num=20005;

select sum(item_price * quantity) as total_price
from orderitems
where order_num=20005;

–聚集不同值:distinct不能用于count(*)
select AVG(distinct prod_price) as avg_prce
from Products
where vend_id=‘DLL01’;

–组合聚集函数
select COUNT(*) as num_items,
MIN(prod_price) as price_min,
MAX(prod_price) as price_max,
AVG(prod_price) as price_avg
from Products;

–创建分组：group by子句中必须是检索列或有效的表达式，且必须出现在where之后，order by 之前
select vend_id,COUNT(*) as num_prods
from Products
group by vend_id;

–过滤分组having
select cust_id,COUNT () as orders
from Orders
group by cust_id
having COUNT()>=2; --having需与group by结合使用

select vend_id,COUNT() as num_prods
from Products
where prod_price >=4
group by vend_id
having COUNT()>=2; --having过滤分组，where过滤行

–分组和排序：group by 和 order by
select order_num,COUNT() as items
from OrderItems
group by order_num
having COUNT()>=3;

select order_num,COUNT() as items
from OrderItems
group by order_num
having COUNT()>=3
order by items,order_num;
/*select 子句及顺序
1 select 必须
2 from 仅在从表选择数据时使用
3 where 非必须
4 group by 仅在按组计算聚集时使用
5 having 非必须
6 order by 非必须 */

–利用子查询进行过滤
select cust_name,cust_contact–3
from Customers
where cust_id in (select cust_id --2
from Orders
where order_num in (select order_num --1
from OrderItems
where prod_id=‘RGAN01’ )) --非最有效方法

–作为计算字段使用子查询
select cust_name,
cust_state,
(select COUNT(*)
from Orders
where Orders.cust_id=Customers.cust_id) as orders
from Customers
order by cust_name

–创建联结
select vend_name,prod_name,prod_price
from Vendors,Products
where vendors.vend_id=products.vend_id; --等值联结

–内联结
select vend_name,prod_name,prod_price
from Vendors inner join Products
on vendors.vend_id=products.vend_id;

–联结多个表
select prod_name,vend_name,prod_price,quantity
from OrderItems,Products,Vendors
where products.vend_id=vendors.vend_id
and orderitems.prod_id=Products.prod_id
and order_num=20007;

–子查询及联结的比较
select cust_name,cust_contact
from Customers,Orders,OrderItems
where customers.cust_id=orders.cust_id
and orders.order_num=orderitems.order_num
and orderitems.prod_id=‘RGAN01’;

–使用表别名
select cust_name,cust_contact
from Customers as C,Orders as O,OrderItems as OI
where C.cust_id=O.cust_id
and O.order_num=OI.order_num
and OI.prod_id=‘RGAN01’;

–自联结
select c1.cust_id,c1.cust_name,c1.cust_contact
from Customers c1,Customers c2
where c1.cust_name=c2.cust_name
and c2.cust_contact=‘Jim Jones’; --一般情况下,联结的处理效率比子查询快

–自然联结
select C.*,O.order_num,O.order_date,
OI.prod_id,OI.quantity,OI.item_price
from Customers as C,Orders as O,OrderItems as OI
where C.cust_id=O.cust_id
and OI.order_num=O.order_num
and prod_id=‘RGAN01’;

–外联结
select c.cust_id,o.order_num
from Customers c inner join Orders o
on c.cust_id=o.cust_id; --内联结

select c.cust_id,o.order_num
from Customers c left outer join Orders o
on c.cust_id=o.cust_id; --左外联结

select c.cust_id,o.order_num
from Customers c right outer join Orders o
on c.cust_id=o.cust_id; --右外联结
/调整from或where子句中表的顺序,左外和右外可以转换/

select c.cust_id,o.order_num
from Customers c full outer join Orders o
on c.cust_id=o.cust_id; --全外联结

–交叉联结:没有where子句,结果产生笛卡尔积
select c.cust_id,o.order_num
from Customers c cross join Orders o;

select c.cust_id,o.order_num
from Customers c,Orders o; --产生结果与交叉联结结果一样

–使用带聚集函数的联结
select c.cust_id,
COUNT(o.order_num) as num_ord
from Customers C inner join Orders O
on c.cust_id=o.cust_id
group by c.cust_id;

select c.cust_id,
COUNT(o.order_num) as num_ord
from Customers C left outer join Orders O
on c.cust_id=o.cust_id
group by c.cust_id;

–创建组合查询
select cust_name,cust_contact,cust_email
from Customers
where cust_state in (‘IL’,‘IN’,‘MI’)
union
select cust_name,cust_contact,cust_email
from Customers
where cust_name = ‘Fun4All’; --自动删除重复行

select cust_name,cust_contact,cust_email
from Customers
where cust_state in (‘IL’,‘IN’,‘MI’)
or cust_name = ‘Fun4All’; --输出结果与上面union相同

–包含或取消重复的行
select cust_name,cust_contact,cust_email
from Customers
where cust_state in (‘IL’,‘IN’,‘MI’)
union all
select cust_name,cust_contact,cust_email
from Customers
where cust_name = ‘Fun4All’;

–对组合查询结果排序
select cust_name,cust_contact,cust_email
from Customers
where cust_state in (‘IL’,‘IN’,‘MI’)
union
select cust_name,cust_contact,cust_email
from Customers
where cust_name = ‘Fun4All’
order by cust_name,cust_contact; --只能存在一条order by子句，且放在最后

---------------------------------------------------------------数据库表操作部分-------------------------------------------------------

–1.插入数据（insert）

–插入完整的行
insert into Customers
values(‘1000000006’,
‘Toy Land’,
‘123 Any Street’,
‘New York’,
‘NY’,
‘11111’,
‘USA’,
null,
null); --依赖于特定列次序

insert into Customers(cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email)
values(‘1000000006’,
‘Toy Land’,
‘123 Any Street’,
‘New York’,
‘NY’,
‘11111’,
‘USA’,
null,
null); --不依赖于特定列次序,即使表结构改变也可以正确执行

–插入部分行
insert into Customers(cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country)
values(‘1000000006’,
‘Toy Land’,
‘123 Any Street’,
‘New York’,
‘NY’,
‘11111’,
‘USA’); --明确给出列名,该列允许null值或默认值

–插入检索出的数据
insert into Customers(cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email)
select cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email
from CustNew
where cust_id=‘1000000010’; --select的列名不要求匹配insert列名,使用的是select中列的位置

/insert into Customers(cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email)
select cust_id,
cust_country,
cust_contact,
cust_city,
cust_state,
cust_zip,
cust_name,
cust_address,
cust_email
from CustNew
where cust_id=‘1000000011’;/

–从一个表复制到另一个表:运行中创建表
select *
into CustCopy
from Customers;

–2.更新和删除数据（update、delete）

–更新数据
update Customers
set cust_email=‘kim@thetoystore.com’
where cust_id=‘1000000005’;

update Customers
set cust_contact=‘Sam Roberts’,
cust_email=‘sam@toyland.com’
where cust_id=‘1000000006’;

update Customers
set cust_email=null
where cust_id=‘1000000005’; --删除某列的值

–删除数据
delete from Customers
where cust_id=‘1000000010’;

–更快的删除
truncate table custcopy;

–3.创建表

–创建表create
CREATE TABLE ProductsCopy
(
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
);

–使用null值
CREATE TABLE VendorsCopy
(
vend_id char(10) NOT NULL ,
vend_name char(50) NOT NULL ,
vend_address char(50) ,
vend_city char(50) ,
vend_state char(5) ,
vend_zip char(10) ,
vend_country char(50)
); --null为默认设置

–指定默认值default
CREATE TABLE OrderItemsCopy
(
order_num int NOT NULL ,
order_item int NOT NULL ,
prod_id char(10) NOT NULL ,
quantity int NOT NULL default 1,
item_price decimal(8,2) NOT NULL
);

–更新表alter
alter table vendors
add vend_phone char(20);
–删除
alter table vendors
drop column vend_phone;

–删除表drop
drop table CustCopy;

–重命名表:使用存储过程sp_rename
EXEC sp_rename ‘VendorsCopy’, ‘vendorscop’
–重命名列
EXEC sp_rename ‘vendorscop.[vend_city]’, ‘city’, ‘COLUMN’
–注意: 更改对象名的任一部分都可能会破坏脚本和存储过程。

–4.使用视图

–创建视图create view
create view ProductCustomers as
select cust_name,cust_contact,prod_id
from Customers as C,Orders as O,OrderItems as OI
where C.cust_id=O.cust_id
and O.order_num=OI.order_num;

–查询
select cust_name,cust_contact
from ProductCustomers
where prod_id=‘RGAN01’;

–删除视图
drop view ProductCustomers;

–用视图重新格式化检索出的数据
create view VendorseLocations as
select rtrim(vend_name)+’(’+rtrim(vend_country)+’)’
as vend_title
from Vendors;

select * from VendorseLocations;

–用视图过滤不想要的数据
create view CustomerEMailList as
select cust_id,cust_name,cust_email
from Customers
where cust_email is not null;

–使用视图与计算字段
create view OrderItemsExpanded as
select prod_id,
quantity,
item_price,
quantity*item_price as expanded_price
from OrderItems;

–5.使用存储过程

–执行存储过程
execute AddNewProduct(‘JTS01’,
‘Stuffed Eiffel Tower’,
6.49,
‘Plush Stuffed toy with the text La
Tower Eiffel in red white and blue’); --未创建此存储过程不能执行

–创建存储过程
create procedure MailingListCount
as
declare @cnt integer
select @cnt = COUNT(*)
from Customers
where not cust_email is null;
return @cnt;
–调用
declare @ReturnValue int
execute @ReturnValue=MailingListCount;
select @ReturnValue;

–创建新订单
create procedure NewOrder @cust_id char(10)
as
declare @order_num integer --声明一个变量来存储订单号
select @order_num=MAX(order_num) --检索当前最大订单号
from Orders
select @order_num=@order_num+1 --订单号增加1
insert into Orders(order_num,order_date,cust_id) --插入新订单
values(@order_num,GETDATE(),@cust_id)
return @order_num; --返回订单号

–创建新订单(与上一条相同)：自动生成订单号，使用全局变量@@IDENTITY
create procedure NewOrder @cust_id char(10)
as
insert into Orders(cust_id) --插入新订单
values(@cust_id)
select order_num =@@IDENTITY; --返回订单号

–调用
declare @OrderNum int
execute @OrderNum=NewOrder @cust_id=1000000001; --直接赋予顾客id，取系统当前时间
select * from Orders;

–6.管理事务处理
/*概念：
1.事务（transaction）指一组SQL语将句；
2.回退（rollback）只撤销指定SQL语句的过程；可以回退insert、update、delete；
3.提交（commit）指将未存储的SQL语句结果写入数据库表；
4.保留点（savepoint）指事务处理中设置的临时占位符（placeholder），可以对它发布回退（与回退整个事务处理不同）。 */

–使用rollback
begin transaction
delete from OrderItems;
rollback transaction;

–使用commit
begin transaction
delete OrderItems where order_num=20001
delete Orders where order_num=20006
commit transaction; --必须两条delete都成功才提交

–使用保留点(占位符)
save transaction delete1;
rollback transaction delete1;

begin transaction
insert into Customers(cust_id,cust_name)
values(‘1000000012’,‘Toys Emporium’);
save transaction StartOrder; --保留点
insert into Orders(order_num, order_date, cust_id)
values(20101,‘2001/12/1’,‘1000000012’);
if @@ERROR <> 0
rollback transaction StartOrder; --变量@@ERROR返回非0的值，表示有错误发生
insert into OrderItems(order_num,order_item,prod_id,quantity,item_price)
values(20102,1,‘BR01’,100,5.49);
if @@ERROR <> 0
rollback transaction StartOrder;
insert into OrderItems(order_num,order_item,prod_id,quantity,item_price)
values(20100,2,‘BR03’,100,10.99);
if @@ERROR <> 0
rollback transaction StartOrder;
commit transaction ;
–无法回滚 StartOrder。找不到该名称的事务或保存点。？？？

/*删除新增数据重新插入数据
delete from OrderItems
delete from Orders
delete from Customers

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 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); */

–7.使用游标

–创建游标
declare CustCursor CURSOR
for
select * from Customers
where cust_email is null;

–使用游标
OPEN CustCursor;
FETCH …

–关闭游标
CLOSE CustCursor;

–例子
declare CustCursor CURSOR --创建
for
select * from Customers
where cust_email is null
declare @cust_id char(10),
@cust_name char(50),
@cust_address char(50),
@cust_city char(50),
@cust_state char(5),
@cust_zip char(10),
@cust_country char(50),
@cust_contact char(50),
@cust_email char(255)
OPEN CustCursor --使用
fetch next from CustCursor --检索一行并保存到声明的变量中
into @cust_id,@cust_name,@cust_address,
@cust_city,@cust_state,@cust_zip,
@cust_country,@cust_contact,@cust_email
while @@FETCH_STATUS = 0 --循环，取不出更多行时终止（退出循环）
begin

fetch next from CustCursor
into @cust_id,@cust_name,@cust_address,
@cust_city,@cust_state,@cust_zip,
@cust_country,@cust_contact,@cust_email
update Customers --使用具体的处理代码,
set cust_email=‘kim@thetoystore.com’ --为什么每一行都插入了???
end

close CustCursor;

–8.约束

–主键
/满足条件：
1.任意两行的主键值都不同；
2.每行都具有一个主键值（即列中不允许null值）；
3.包含主键值的列从不修改或更新；
4.主键值不能重用。如果从表中删除某一行，其主键值不分配给新行。/

–创建主键
CREATE TABLE VendorsCopy
(
vend_id char(10) NOT NULL PRIMARY KEY, --系统随机主键名
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
);

–删除主键
alter table VendorsCopy
drop constraint PK__VendorsC__32BF447E22AA2996;

–创建主键
alter table VendorsCopy
add constraint pk_vendorscopy
primary key(vend_id);

–外键
–创建外键
CREATE TABLE OrdersCopy
(
order_num int NOT NULL primary key,
order_date datetime NOT NULL ,
cust_id char(10) NOT NULL references Customers(cust_id)
);

alter table OrdersCopy
add constraint fk_orderscop
foreign key(cust_id) references Customers(cust_id); --可重复建外键???

–唯一约束
/*与主键的区别：
1.表可包含多个唯一约束,但每个表只允许一个主键;
2.唯一约束可包含null值；
3.唯一约束列可修改或更新；
4.唯一约束列的值可重复使用；
5.与主键不一样，唯一约束列不能用来定义外键。 */

–创建唯一约束
CREATE TABLE Employees
(
emp_id char(10) NOT NULL PRIMARY KEY,
emp_name char(50) NOT NULL ,
emp_sex char(2) NULL ,
emp_idcard char(18) NOT NULL UNIQUE,
emp_nation char(50) NULL
);

alter table Employees
add constraint UQ_idcard
unique (emp_idcard); --重复???

–检查约束
/*用途：
1.检查最大值最小值,如防止0个物品的订单(及时0是合法数);
2.指定范围,如保证发货日期大于等于今天的日期,但不超过今天起一年后的日期；
3.值允许特定的值,如性别字段中值允许M或F。 */

–创建检查约束
CREATE TABLE OrderItemsCopy
(
order_num int NOT NULL ,
order_item int NOT NULL ,
prod_id char(10) NOT NULL ,
quantity int NOT NULL check (quantity > 0),
item_price decimal(8,2) NOT NULL
);

alter table Employees
add constraint CK_sex
check (emp_sex like ‘[MF]’); --[]通配符表示数据集

–索引:用于数据过滤及排序
–创建
create index prod_name_ind
on products (prod_name);

–触发器:用于update,insert,delete
/*用途：
1.保证数据一致；
2.基于某个表的变动在其他表上执行活动；
3.进行额外的验证并根据需要回退数据；
4.计算计算列的值或更新时间戳。 */

–创建
create trigger customer_state
on customers
for insert,update
as
update Customers
set cust_state = UPPER(cust_state)
where Customers.cust_id=(select cust_id from inserted);

–验证
insert into Customers
values(‘1000000010’,
‘Toy Land’,
‘123 Any Street’,
‘Beijing’,
‘bj’,
‘11111’,
‘CHINA’,
null,
null);

–数据库安全：grant(授权) 、revoke(回收权限)

/*
1)授权命令 grant
Grant <权限> on 表名[(列名)] to 用户 With grant option
或 GRANT <权限> ON <数据对象> FROM <数据库用户>

数据对象可以是表名或列名
权限表示对表的操作，如select,update,insert,delete
注：授权命令是由数据库管理员使用的，若给用户分配权限时带With grant option子句，
则普通用户获权后,可把自己的权限授予其他用户。

2)回收权限 revoke
REVOKE <权限> ON <数据对象> FROM <数据库用户名> */

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