select from Category
    go
    —go—用于执行批处理代码
    select     from Product
    —declare 用于声明变量
    declare @a int
    declare @b int

    —设置（赋值）
    set @a=1s
    print @a
    select @a
    —2
    declare @c varchar(50)
    declare @d money
    select top 1 @c= ProductName,@d=Price from Product order by Price desc
    print @c
    print @d

    —输出
    —print
    —select

    —请打印卖得最多的商品名称
    declare @id int ,@cc varchar(50)
    select top 1 @id=Productid from OrderDetails
    group by ProductID
    order by sum(Quantity) desc
    select @cc=ProductName from Product where ProductID=@id
    print @cc

    ————————————————-全局变量 @@(双@符号)——————————————————-
    —@@identity 获取上一次操作的主键(id)身份
    —@@rowcount 获取上一次操作的影响行
    —insert into Product (ProductID)values(‘小陈’)
    —select @@identity
    —select @@rowcount

    print @@error ——-获取错误编写
    print @@language ——-获取数据库语言
    print @@version ——-获取系统版本和数据库版本
    print @@servername ——-获取服务器名称

    if(1=1)
    begin —开始
    print(‘真的’)
    end —结束
    else
    begin
    print(‘假的’)
    end

    if exists(select * from Product where Price=49)
    begin
    print(‘有’)
    end
    else
    begin
    print(‘没有’)
    end

    select * from Category

    —查询一下“儿童玩具”分类属于那个大分类
    select *from Category a right outer join Category b on a.CategoryID=b.P_Cate where b.CategoryName=’儿童玩具’

    select * from Category
    select Categoryid,CategoryName,
    case p_cate
    when 1 then ‘母婴’
    when 2 then ‘手机数码’
    when 3 then ‘箱包’
    when 4 then ‘百货’
    else ‘其他’ end as ‘类别’
    from Category

    —当客户是男的,就显示先生，否则就显示女士
    select Customername,
    case gender
    when ‘男’ then’公子’
    when ‘女’ then ‘小姐’ end as ‘称呼’
    from Customer

    ————————-100元以下显示便宜，100到200显示一般，大于200显示很贵
    select Productname,price,
    case
    when price<100 then '便宜'
    when price<=200 then ‘一般’
    when price>200 then ‘很贵’ end as ‘贵不贵’ from Product

    —-循环while——————————————————————-
    print ‘嘉嘉是个大帅哥’
    declare @aa int
    set @aa=0
    while (@aa<5)
    begin
    print ‘嘉嘉是个大帅哥’
    set @aa=@aa+1
    end

    —-输出从十到一————————————
    declare @bb int
    set @bb=10
    while (@bb>0)
    begin
    print @bb
    set @bb=@bb-1
    end

    —小练习：输出20以内能被3整除的数
    declare @dd int
    set @dd=20
    while (@dd>0)
    begin
    if @dd%3=0
    begin
    print @dd
    end
    set @dd=@dd-1
    end

    —输出10以内的偶数
    declare @ee int
    set @ee=10
    while (@ee>0)
    begin
    if @ee%2=1
    begin
    set @ee=@ee-1
    continue
    end
    else
    begin
    print @ee
    set @ee=@ee-1
    end
    end