我有一个表格,其中有一列名为“Faktor”(varchar(50)),其中包含以下表达式:
1/3
2*9/5
0.567
0.23
不,我正在寻找一种类似select的执行方式。
select Faktor from Artikel
应该返回一个类型为小数的列,其值为:
0.333333
3.6
0.567
0.23
我有一个表格,其中有一列名为“Faktor”(varchar(50)),其中包含以下表达式:
1/3
2*9/5
0.567
0.23
select Faktor from Artikel
0.333333
3.6
0.567
0.23
我会选择一个CLR,比如这个(它具有在SET操作中工作的优势,而动态SQL替代品(例如Abduls答案)则不会):
编辑: CLR dll的源代码(Visual Studio 2008)发布在此处:http://www.heavencore.co.uk/filehub/uploaded/EvalFunction.zip
如果您更喜欢编译程序集,这里是代码:
Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Data.SqlTypes
Imports Microsoft.SqlServer.Server
Imports System.Runtime.InteropServices
Partial Public Class UserDefinedFunctions
<Microsoft.SqlServer.Server.SqlFunction()> _
Public Shared Function EVAL(ByVal InputExpression As SqlString) As SqlDecimal
Return Evaluate(InputExpression)
End Function
Private Shared Function Evaluate(ByVal expression As SqlString) As SqlDecimal
Dim expressionStr As String = expression.ToString()
Dim loDataTable = New DataTable()
Dim loDataColumn = New DataColumn("Eval", GetType(Double), expressionStr)
loDataTable.Columns.Add(loDataColumn)
loDataTable.Rows.Add(0)
Return ParseDecimal(loDataTable.Rows(0)("Eval").ToString(), 0)
End Function
Public Shared Function ParseDecimal(ByVal InputStr As String, Optional ByVal ReturnIfFail As Decimal = 0) As Decimal
Dim ParseOutput As Decimal = 0
If Decimal.TryParse(InputStr, ParseOutput) = False Then
Return ReturnIfFail
Else
Return ParseOutput
End If
End Function
End Class
SELECT Faktor, dbo.Eval(Faktor) as Result FROM Artikel
编辑:好的,我刚刚测试了一下,在基于集合的操作等方面它能够良好地工作,安装步骤如下:
-- Enable the CLR to run user-defined functions
EXEC sp_configure
'clr enabled' ,
'1'
GO
RECONFIGURE
GO
-- Set the appropriate database security permission
ALTER DATABASE [TargetDatabase] SET TRUSTWORTHY ON
GO
-- Import the assembly
CREATE ASSEMBLY EvalFunction
FROM 'C:\bin\EvalFunction.dll'
WITH PERMISSION_SET = EXTERNAL_ACCESS;
GO
-- Create the Eval function for easy use
CREATE FUNCTION dbo.Eval
(
@Expression NVARCHAR(255)
)
RETURNS DECIMAL(18, 2)
AS EXTERNAL NAME
EvalFunction.[EvalFunction.UserDefinedFunctions].EVAL
GO
declare @expr nvarchar(10)
set @expr='2*9/5'
declare @query varchar(800)
BEGIN TRY
SELECT CAST(@expr as decimal(5,2))
END TRY
BEGIN CATCH
SET @query='SELECT CAST('+@expr+'.0 as decimal(5,2))'
EXECUTE(@query)
END CATCH