Question

我正在使用带有SQL Server 2012数据库的vb.net。

我想检查数据库中文件列表的状态。查询很简单，就像这样。

DECLARE @Filename NVARCHAR(100)

SET @Filename = 'MyFileName.doc'

SELECT DISTINCT 
    Docs.Filename,
    Status.Name as 'Status'
FROM 
    [Documents] AS Docs
INNER JOIN 
    [Status] AS Status ON Status.StatusID = Docs.CurrentStatusID
WHERE 
    Docs.Filename LIKE @Filename

它适用于一个文件名，我可以使用sql连接在vb.net中轻松启动它，如本例所示。

Dim conn As New SqlConnection
If conn.State = ConnectionState.Closed Then
    conn.ConnectionString = PDMConnectionString
End If

Try
    conn.Open()
    Dim sqlquery As String =
        "DECLARE @Filename NVARCHAR(100)
         SELECT DISTINCT 
         Docs.Filename,
         Status.Name as 'Status'

         FROM [Documents] AS Docs
         INNER JOIN [Status] AS Status
         ON Status.StatusID = Docs.CurrentStatusID

         WHERE Docs.Filename LIKE @Filename  "

    Dim data As SqlDataReader
    Dim adapter As New SqlDataAdapter
    Dim parameter As New SqlParameter
    Dim command As SqlCommand = New SqlCommand(sqlquery, conn)
    With command.Parameters
        .Add(New SqlParameter("@filename", "MyFileName.doc"))
    End With
    command.Connection = conn
    adapter.SelectCommand = command
    data = command.ExecuteReader()
    While data.Read
         'do something'
    End While
Catch ex As Exception

End Try

问题是我需要找到很多文件的状态，我只想用一个查询来做。

我可以直接在查询中通过更改最后一行来这样做，删除vb.net中的参数并直接发送查询：

WHERE 
    Docs.Filename IN ('MyFileName.doc', 'MyOtherFileName.doc')

但它意味着很多字符串连接，我不太喜欢该解决方案的代码。

在这种情况下使用的最佳做法是什么，以便使用较少的字符串连接并使代码更易于管理？

Answer 1

您可以使用函数来获取逗号分隔的字符串并返回表格...

let uniqueProcessPool = WKProcessPool()

let configA = WKWebViewConfiguration()
configA.processPool = uniqueProcessPool
let webViewA = init(frame: CGRect.zero, configuration: configA)

let configB = WKWebViewConfiguration()
configB.processPool = uniqueProcessPool
let webViewB = init(frame: CGRect.zero, configuration: configB)

然后在你的SQL中加入它......

CREATE FUNCTION [dbo].[FileNames]( @FilenameValues nvarchar(max) )
RETURNS  @Result TABLE( FileName nvarchar(max) )
AS
BEGIN

        -- convert to an xml string
        DECLARE @xml XML 
        SELECT @xml = CAST( '<A>' + REPLACE( @FilenameValues, ',', '</A><A>' ) + '</A>' AS XML )

        -- select rows out of the xml string
        INSERT INTO @Result            
        SELECT DISTINCT LTRIM( RTRIM( t.value( '.', 'nvarchar(max)' ) ) ) AS [FileName]
        FROM @xml.nodes( '/A ') AS x(t)

        RETURN

   END

或在WHERE中使用......

JOIN (
    SELECT * FROM dbo.FileNames( 'MyFileName.doc, MyOtherFileName.doc' )
) FileNames ON FileNames.FileName = Docs.Filename

使用vb.net在SQL查询中将列表作为输入传递的最佳实践

1 个答案: