动态创建列sql

Posted 2023-02-16

【中文标题】动态创建列sql

【英文标题】：Dynamically create columns sql

【发布时间】：2012-09-20 12:31:45

【问题描述】：

我有一张客户表

Customer ID        Name         
   1               John        
   2               Lewis        
   3               Mary         

我有另一张表 CustomerRewards

 TypeID           Description
   1                Bronze
   2                Silver
   3                Gold
   4               Platinum
   5               AnotherOne

决赛桌

 RewardID          TypeID          CustomerID
    1                1                 1
    2                1                 1
    3                2                 1
    4                2                 2

customerTypes 表是动态的，其中许多类型可以添加和删除。基本上我想要的只是动态生成的列和每个列的计数，比如

CustomerName        Bronze        Silver     Gold      Platinum     AnotherOne    total
   John               2             1         0           0             0           3
   Lewis              0             1         0           0             0           1
 Grand TOTAL          2             2         0           0             0           4

问题就像我说的那样，类型是动态的，客户是动态的，所以我需要根据系统中的类型动态列

我已经在 DataGridView 中标记了 c#，因为我需要它

提前致谢

【问题讨论】：

这看起来像一个支点。我已经做了一些，但我无法从记忆中输入一个。也许是通过在 SQL 端旋转数据创建的数据库中的视图？

如果您需要在 SQL 中执行此操作，您可能需要动态数据透视。参见，例如，simple-talk.com/blogs/2007/09/14/… 但这并不是一个真正干净的解决方案。如果您可以等待将数据导入 C#，您可以使用 LINQ 来执行此操作。

这些看起来确实很复杂！感谢 cmets，我会研究 Pivot，但如果有人有简单的解决方案，请随意

SQL Server dynamic PIVOT query?的可能重复

【参考方案1】：

您需要为此使用PIVOT 函数。如果您有已知数量的列，那么您可以对这些值进行硬编码：

select name, [Bronze], [Silver], [Gold], [Platinum], [AnotherOne]
from
(
  select c.name,
    cr.description,
    r.typeid
  from customers c
  left join rewards r
    on c.id = r.customerid
  left join customerrewards cr
    on r.typeid = cr.typeid
) x
pivot
(
  count(typeid)
  for description in ([Bronze], [Silver], [Gold], [Platinum], [AnotherOne])
) p;

见SQL Fiddle with Demo。

现在如果你有未知数量的列，那么你可以使用动态 SQL 来PIVOT：

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT ',' + QUOTENAME(description) 
                    from customerrewards
                    group by description, typeid
                    order by typeid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT name,' + @cols + ' from 
             (
                select c.name,
                  cr.description,
                  r.typeid
                from customers c
                left join rewards r
                  on c.id = r.customerid
                left join customerrewards cr
                  on r.typeid = cr.typeid
            ) x
            pivot 
            (
                count(typeid)
                for description in (' + @cols + ')
            ) p '

execute(@query)

见SQL Fiddle With Demo

如果您需要包含Total 列，则可以使用ROLLUP (Static Version Demo)：

select name, sum([Bronze]) Bronze, sum([Silver]) Silver, 
  sum([Gold]) Gold, sum([Platinum]) Platinum, sum([AnotherOne]) AnotherOne
from 
(
  select name, [Bronze], [Silver], [Gold], [Platinum], [AnotherOne]
  from
  (
    select c.name,
      cr.description,
      r.typeid
    from customers c
    left join rewards r
      on c.id = r.customerid
    left join customerrewards cr
      on r.typeid = cr.typeid
  ) x
  pivot
  (
    count(typeid)
    for description in ([Bronze], [Silver], [Gold], [Platinum], [AnotherOne])
  ) p
) x
group by name with rollup

动态版（Demo）：

DECLARE @cols AS NVARCHAR(MAX),
    @colsRollup AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT ',' + QUOTENAME(description) 
                    from customerrewards
                    group by description, typeid
                    order by typeid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

select @colsRollup 
      = STUFF((SELECT ', Sum(' + QUOTENAME(description) + ') as '+ QUOTENAME(description)
                    from customerrewards
                    group by description, typeid
                    order by typeid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')


set @query 
          = 'SELECT name, '+ @colsRollup + '
             FROM
             (
                SELECT name,' + @cols + ' from 
                 (
                    select c.name,
                      cr.description,
                      r.typeid
                    from customers c
                    left join rewards r
                      on c.id = r.customerid
                    left join customerrewards cr
                      on r.typeid = cr.typeid
                ) x
                pivot 
                (
                    count(typeid)
                    for description in (' + @cols + ')
                ) p 
              ) x1
              GROUP BY name with ROLLUP'

execute(@query)

【讨论】：

你有一个 SQL 注入缺陷/可用性错误： = STUFF((SELECT ', Sum(' + QUOTENAME(description) + ') as '+ description 应该是： = STUFF((SELECT ', Sum(' + QUOTENAME(description) + ') as '+ QUOTENAME(description) 否则，这是一个很棒的帖子！

@shellster 是的，你是对的。我更新了我的代码。感谢您了解这一点。