Question

在买表中。当客户购买同一本书1行添加到表。因此，当在购买页面中看到购买清单时，就像这样：

buy1 price1 downloadlink1
buy1 price1 downloadlink1
buy1 price1 downloadlink1
buy2 price2 downloadlink2
buy2 price2 downloadlink2
buy2 price2 downloadlink2

但我希望在同一行价格和downloadlink删除，只有第一行显示此值像这样：

buy1 price1 downloadlink1
buy1 
buy1 
buy2 price2 downloadlink2
buy2 
buy2

我怎样才能使用sql查询???

Answer 1

如果它是MS SQL服务器，我建议使用row_number over() 但在你的情况下，我可以建议尝试这个（我想你的表中有一些id）

select
    A.sub,
    case when A.frst = 1 then A.user else null end as user,
    case when A.frst = 1 then A.versionid else null end as versionid,
    case when A.frst = 1 then A.hard else null end as hard,
    case when A.frst = 1 then A.active else null end as active,
    case when A.frst = 1 then A.res else null end as res
from
(
    select
        *,
        case
            when exists
            (
                select * 
                from buy as tt
                where
                    tt.sub = t.sub and tt.res = t.res and
                    tt.user = t.user and tt.versionid = t.versionid and
                    tt.hard = t.hard and tt.active = t.active and
                    tt.id < t.id
            ) then 0
            else 1
        end as frst
    from buy as t
) as A
order by A.sub, A.frst desc

SQL FIDDLE

Answer 2

在执行下载链接时在SQL查询中使用distinct

Answer 3

如果该用户未添加该特定项目，则向表中添加行   进入表格

如果该项已经存在（使用item id和userid检查）更新   表

找到相同的表行

3 个答案: