在SQL视图中使用coce

Question

我需要从几个表创建视图。视图中的一列必须由一个带有逗号分隔值的字符串从表中的一个行组成。

这是我想做的简化示例。

Customers:
CustomerId int
CustomerName VARCHAR(100)

Orders:
CustomerId int
OrderName VARCHAR(100)

客户和订单之间存在一对多关系。因此，鉴于此数据

Customers
1 'John'
2 'Marry'

Orders
1 'New Hat'
1 'New Book'
1 'New Phone'

我希望有这样的视图：

Name     Orders
'John'   New Hat, New Book, New Phone
'Marry'  NULL

因此，无论他们是否有订单，每个人都会出现在桌子上。

我有一个存储过程，需要转换为此视图，但是似乎您无法在视图中声明参数并调用存储的procs。关于如何将此查询置入视图的任何建议？

CREATE PROCEDURE getCustomerOrders(@customerId int)
AS
   DECLARE @CustomerName varchar(100)
   DECLARE @Orders varchar (5000)

   SELECT @Orders=COALESCE(@Orders,'') + COALESCE(OrderName,'') + ',' 
   FROM Orders WHERE CustomerId=@customerId

   -- this has to be done separately in case orders returns NULL, so no customers are excluded
   SELECT @CustomerName=CustomerName FROM Customers WHERE CustomerId=@customerId

   SELECT @CustomerName as CustomerName, @Orders as Orders

Answer 1

编辑: ：修改的答案以包括视图的创建。

/* Set up sample data */
create table Customers (
    CustomerId int,
    CustomerName VARCHAR(100)
)

create table Orders (
    CustomerId int,
    OrderName VARCHAR(100)
)

insert into Customers
    (CustomerId, CustomerName)
    select 1, 'John' union all
    select 2, 'Marry'

insert into Orders
    (CustomerId, OrderName)
    select 1, 'New Hat' union all
    select 1, 'New Book' union all
    select 1, 'New Phone'
go

/* Create the view */       
create view OrderView as    
    select c.CustomerName, x.OrderNames
        from Customers c
            cross apply (select stuff((select ',' + OrderName from Orders o where o.CustomerId = c.CustomerId for xml path('')),1,1,'') as OrderNames) x
go

/* Demo the view */
select * from OrderView
go 

/* Clean up after demo */
drop view OrderView
drop table Customers
drop table Orders
go

Answer 2

在SQL Server 2008中，您可以利用XML添加的某些功能，以一次查询完成此操作，而无需使用存储的Proc：

 SELECT CustomerName,
    STUFF( -- "STUFF" deletes the leading ', '
        ( SELECT ', ' + OrderName
        FROM Orders
        WHERE CustomerId = Customers.CutomerId
        -- This causes the sub-select to be returned as a concatenated string
        FOR XML PATH('') 
        ),
    1, 2, '' )
    AS Orders
 FROM Customers