Question

我使用EAV模式在单个表（Entries）中存储任意数据。 Data存储为nvarchar，并通过PropertyID链接目标数据类型。现在我想创建一个使用pivot重构数据的视图，但是我无法动态地将Data转换为其预期的数据类型。执行下面的查询，我收到错误#8114 error converting data type nvarchar to float。

这基本上是我的数据库结构：

EntryID | PropertyID | Data (nvarchar)
----------------------------
1       | 1          | 1
2       | 2          | abc
3       | 3          | 2.0
....


PropertyID | PropertyName | TypeID
------------------------------------
1          | intProp      | 1
2          | strProp      | 2
3          | fltProp      | 3
....

TypeID | TypeName
-----------------
1      | int
2      | string
3      | float
4      | bool
5      | datetime
....

这是查询：

SELECT [intProp], [strProp], [fltProp]
FROM
(
    SELECT e.EntryID, p.PropertyName, 

        CASE 
            WHEN t.TypeName = 'int' THEN
                CAST(e.data as int)
            WHEN t.TypeName = 'float' THEN
                CAST(e.data as float)
            WHEN t.TypeName = 'string' THEN
                e.data

        END as converted

    FROM 
        Entries e 
        INNER JOIN Properties p ON e.PropertyID = p.PropertyID
        INNER JOIN Types t ON p.TypeID = t.TypeID           
) as t1
PIVOT
(
    MAX(converted)
    FOR PropertyName IN ( [intProp], [strProp], [fltProp])
) as piv

显然CASE语句是问题所在，但是如何将查询转换为动态转换为正确的数据类型？

Answer 1

根据我之前的评论，我尝试创建一个可能对您有帮助的SQL脚本：

    DECLARE @colsConversion as NVARCHAR(MAX), @query AS NVARCHAR(MAX)
    SELECT @colsConversion = STUFF((SELECT ',CAST('+QuoteName(p.PropertyName)+' as '+t.TypeName+') as '+QuoteName(p.PropertyName)
    FROM  Properties  p 
    INNER JOIN Types t ON p.TypeID = t.TypeID
    GROUP BY p.PropertyName, t.TypeName
    FOR XML PATH(''),TYPE).value('.','NVARCHAR(MAX)'),1,1,'')



SET @query = 'SELECT ' + @colsConversion +'
FROM
(
    SELECT e.EntryID,p.PropertyName,t.TypeName
    ,e.Data
    FROM Entries e
    INNER JOIN Properties p ON e.PropertyID = p.PropertyID
    INNER JOIN Types t ON p.TypeID = t.TypeID
)AS T1
PIVOT
(
    MAX(Data)
    FOR PropertyName in ([intProp],[strProp],[fltProp])
)as piv'

exec sp_executesql @query

使用pivot时动态转换

1 个答案: