如何根据显示收入和销售数据的库存数据库编写sql语句？

Question

create table Customer (
   Id                   int                  identity,
   FirstName            nvarchar(40)         not null,
   LastName             nvarchar(40)         not null,
   City                 nvarchar(40)         null,
   Country              nvarchar(40)         null,
   Phone                nvarchar(20)         null,
   constraint PK_CUSTOMER primary key (Id)

create table "Order" (
   Id                   int                  identity,
   OrderDate            datetime             not null default getdate(),
   OrderNumber          nvarchar(10)         null,
   CustomerId           int                  not null,
   TotalAmount          decimal(12,2)        null default 0,
   constraint PK_ORDER primary key (Id)
)

create table OrderItem (
   Id                   int                  identity,
   OrderId              int                  not null,
   ProductId            int                  not null,
   UnitPrice            decimal(12,2)        not null default 0,
   Quantity             int                  not null default 1,
   constraint PK_ORDERITEM primary key (Id)

create table Product (
   Id                   int                  identity,
   ProductName          nvarchar(50)         not null,
   SupplierId           int                  not null,
   UnitPrice            decimal(12,2)        null default 0,
   Package              nvarchar(30)         null,
   IsDiscontinued       bit                  not null default 0,
   constraint PK_PRODUCT primary key (Id)

create table Supplier (
   Id                   int                  identity,
   CompanyName          nvarchar(40)         not null,
   ContactName          nvarchar(50)         null,
   ContactTitle         nvarchar(40)         null,
   City                 nvarchar(40)         null,
   Country              nvarchar(40)         null,
   Phone                nvarchar(30)         null,
   Fax                  nvarchar(30)         null,
   constraint PK_SUPPLIER primary key (Id)
)

INSERT INTO [Customer] ([Id],[FirstName],[LastName],[City],[Country],[Phone])VALUES(6,'Hanna','Moos','Mannheim','Germany','0621-08460')
INSERT INTO [Customer] ([Id],[FirstName],[LastName],[City],[Country],[Phone])VALUES(7,'Frédérique','Citeaux','Strasbourg','France','88.60.15.31')
INSERT INTO [Customer] ([Id],[FirstName],[LastName],[City],[Country],[Phone])VALUES(8,'Martín','Sommer','Madrid','Spain','(91) 555 22 82')

INSERT INTO [Supplier] ([Id],[CompanyName],[ContactName],[City],[Country],[Phone],[Fax])VALUES(4,'Tokyo Traders','Yoshi Nagase','Tokyo','Japan','(03) 3555-5011',NULL)
INSERT INTO [Supplier] ([Id],[CompanyName],[ContactName],[City],[Country],[Phone],[Fax])VALUES(5,'Cooperativa de Quesos ''Las Cabras''','Antonio del Valle Saavedra','Oviedo','Spain','(98) 598 76 54',NULL)
INSERT INTO [Supplier] ([Id],[CompanyName],[ContactName],[City],[Country],[Phone],[Fax])VALUES(6,'Mayumi''s','Mayumi Ohno','Osaka','Japan','(06) 431-7877',NULL)

INSERT INTO [Product] ([Id],[ProductName],[SupplierId],[UnitPrice],[Package],[IsDiscontinued])VALUES(4,'Chef Anton''s Cajun Seasoning',2,22.00,'48 - 6 oz jars',0)
INSERT INTO [Product] ([Id],[ProductName],[SupplierId],[UnitPrice],[Package],[IsDiscontinued])VALUES(5,'Chef Anton''s Gumbo Mix',2,21.35,'36 boxes',1)
INSERT INTO [Product] ([Id],[ProductName],[SupplierId],[UnitPrice],[Package],[IsDiscontinued])VALUES(6,'Grandma''s Boysenberry Spread',3,25.00,'12 - 8 oz jars',0)

INSERT INTO [Order] ([Id],[OrderDate],[CustomerId],[TotalAmount],[OrderNumber])VALUES(5,'Jul  9 2012 12:00:00:000AM',76,3730.00,'542382')
INSERT INTO [Order] ([Id],[OrderDate],[CustomerId],[TotalAmount],[OrderNumber])VALUES(6,'Jul 10 2012 12:00:00:000AM',34,1444.80,'542383')
INSERT INTO [Order] ([Id],[OrderDate],[CustomerId],[TotalAmount],[OrderNumber])VALUES(7,'Jul 11 2012 12:00:00:000AM',14,625.20,'542384')
INSERT INTO [Order] ([Id],[OrderDate],[CustomerId],[TotalAmount],[OrderNumber])VALUES(8,'Jul 12 2012 12:00:00:000AM',68,2490.50,'542385')

INSERT INTO [OrderItem] ([Id],[OrderId],[ProductId],[UnitPrice],[Quantity])VALUES(4,2,14,18.60,9)
INSERT INTO [OrderItem] ([Id],[OrderId],[ProductId],[UnitPrice],[Quantity])VALUES(5,2,51,42.40,40)
INSERT INTO [OrderItem] ([Id],[OrderId],[ProductId],[UnitPrice],[Quantity])VALUES(6,3,41,7.70,10)
INSERT INTO [OrderItem] ([Id],[OrderId],[ProductId],[UnitPrice],[Quantity])VALUES(7,3,51,42.40,35)
INSERT INTO [OrderItem] ([Id],[OrderId],[ProductId],[UnitPrice],[Quantity])VALUES(8,3,65,16.80,15)

我需要协助回答以下问题：

a。每个供应商目前有多少种产品？注意：1 = 停产。

b。 2012、2013和2014年每月订单和收入是多少？结果应该在一张表中。

c。每个客户的总销售额和订单数是多少？