将行数转换为列的可变数目

I'm currently attempting to PIVOT some rows to columns. The problem is that I don't always know how many rows will be available. Let's look at an example:

我目前正在尝试将一些行转向列。问题是，我并不总是知道有多少行可用。让我们看一个例子:

Values_Table                         Columns_Table
------------                         -----------
ID                                   ID
ColumnsTableID                       GroupID
Value                                ColumnName

RESULTS"

结果”

Columns_Table
---------------
ID   |   GroupID   |   ColumnName
---------------------------------     
0        1             Cats
1        1             Dogs
2        1             Birds
3        2             Pontiac
4        2             Ford
5        3             Trex
6        3             Raptor
7        3             Triceratops
8        3             Kentrosaurus

SQL FIDDLE EXAMPLE of a STATIC pivot. I am trying to achieve a dynamic pivot - http://sqlfiddle.com/#!3/2be82/1

一个静态轴心的SQL小提琴示例。我正在尝试实现一个动态的pivot - http://sqlfiddle.com/#

So, here is my dilemma: I want to be able to pivot an unknown number of columns based on, in this scenario, the GroupID.

所以，这里是我的困境:我希望能够在这个场景中，基于，GroupID，基于一个未知的列。

I want to be able to PIVOT, for example, all the rows in GroupID 3 into columns. I would need to do this without knowing how many rows are in groupID 3.

例如，我希望能够将GroupID 3中的所有行转换为列。我需要这样做，而不知道groupID 3中有多少行。

The design of the database is set in stone, so I can't do anything about that. All I can do is work with what I have :(

数据库的设计是一成不变的，所以我对此无能为力。我所能做的就是用我所拥有的去工作

So, that said- does anyone have any suggestions on how to accomplish this task of PIVOTing an unknown number of rows into columns based on, in this example, the groupID?

那么，有人有什么建议来完成这个任务吗?在这个例子中，根据groupID，将未知的行转换成列?

1 个解决方案

#1

If you are not going to know the values ahead of time, then you will need to look at using dynamic SQL. This will create a SQL String that will be executed, this is required because the list of columns must be known when the query is run.

如果您不打算提前知道这些值，那么您需要考虑使用动态SQL。这将创建将要执行的SQL字符串，这是必需的，因为在运行查询时必须知道列的列表。

The code will be similar to:

守则将类似于:

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX),
    @groupid as int

set @groupid = 3

select @cols = STUFF((SELECT distinct ',' + QUOTENAME(GroupName) 
                    from Columns_Table
                    where groupid = @groupid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT ' + @cols + ' 
            from 
            (
              SELECT B.GroupName, A.Value
                , row_number() over(partition by a.ColumnsTableID
                                    order by a.Value) seq
              FROM Values_Table AS A 
              INNER JOIN Columns_Table AS B 
                ON A.ColumnsTableID = B.ID
              where b.groupid = '+cast(@groupid as varchar(10))+' 
            ) p
            pivot 
            (
                min(P.Value)
                for P.GroupName in (' + @cols + ')
            ) p '

execute sp_executesql @query;

See SQL Fiddle with Demo. For groupid of 3, then the result will be:

参见SQL小提琴演示。对于groupid为3，则结果为:

|   KENTROSAURUS |     RAPTOR |     TREX |    TRICERATOPS |
| whatisthiseven | Itsaraptor | Jurassic | landbeforetime |
|         (null) |       zomg |     Park |         (null) |

#1