Question

我对VB.NET更新，我试图在VB.NET中执行SQL查询，但没有在输出中显示任何值。你可以帮我找一下我错的地方。

Dim sConnectionString As String _
    = "User ID=XXX ;Password=XXX;Initial Catalog=gemXXX;Data Source=SCRBAMSDKBXXXXXX"

    Dim objConn As New SqlConnection(sConnectionString)
    objConn.Open()

    Dim sw ,readerObj
    Dim sSQL As String = "select top 1  " & sw & " = e.import  from tblrelcoms r , [beant].[dbo].tblequipments e where r.IDEquipment = e.IDEquipment"
    Using readerObj As SqlClient.SqlDataReader = cmdObj.ExecuteReader
    Dim objCmd As New SqlCommand(sSQL, objConn)
    objCmd.ExecuteNonQuery()

    TextBox1.Text = sw.ToString()

Answer 1

您遇到的问题是，您不能将变量连接到SQL并期望在SQL执行后更新它。

ExecuteScalar可能是实现目标的最简单方法：

Dim sConnectionString As String _
    = "User ID=XXX ;Password=XXX;Initial Catalog=gemXXX;Data Source=SCRBAMSDKBXXXXXX"

Dim sSQL as string = "SELECT TOP 1 e.import  " _
                    "FROM   tblrelcoms r " & _
                    "       INNER JOIN [beant].[dbo].tblequipments e " & _
                    "           ON r.IDEquipment = e.IDEquipment " & _
                    "ORDER BY e.Import;"

Using connection = new SqlConnection(sConnectionString)
    Using command = New SqlCommand(sSQL, connection)

        connection.Open()
        TextBox1.Text = command.ExecuteScalar().ToString()

    End Using
End Using

虽然如果您需要多个列，那么您可以使用数据阅读器：

Dim sConnectionString As String _
    = "User ID=XXX ;Password=XXX;Initial Catalog=gemXXX;Data Source=SCRBAMSDKBXXXXXX"

Dim sSQL as string = "SELECT TOP 1 e.import  " _
                    "FROM   tblrelcoms r " & _
                    "       INNER JOIN [beant].[dbo].tblequipments e " & _
                    "           ON r.IDEquipment = e.IDEquipment " & _
                    "ORDER BY e.Import;"

Using connection = new SqlConnection(sConnectionString)
    Using command = New SqlCommand(sSQL, connection)

        connection.Open()
        Using reader = command.ExecuteReader()

            If reader.Read()
                TextBox1.Text = reader.GetString(0)
            End If
        End Using

    End Using
End Using

我也做了其他一些改变。

添加了Using块以确保IDisposable个对象被正确处置。
将ANSI 89隐式连接的sql连接语法更新为ANSI 92显式连接，因为名称表明您使用的语法已过时24年。开始使用新语法的原因有很多，本文很好地介绍了这一点：Bad habits to kick : using old-style JOINs
在您的sql中添加了ORDER BY子句。没有订单的TOP 1会给你不确定的结果（除非你只有一条记录，在这种情况下，前1名是多余的）

更复杂的解决方案是使用输出参数，这些参数会起作用，看起来更符合您最初想要达到的效果，但对于这种情况（在我看来）是过度的：

Dim sConnectionString As String _
    = "User ID=XXX ;Password=XXX;Initial Catalog=gemXXX;Data Source=SCRBAMSDKBXXXXXX"

Dim sSQL as string = "SELECT TOP 1 @Output = e.import  " _
                    "FROM   tblrelcoms r " & _
                    "       INNER JOIN [beant].[dbo].tblequipments e " & _
                    "           ON r.IDEquipment = e.IDEquipment " & _
                    "ORDER BY e.Import;"

Using connection = new SqlConnection(sConnectionString)
    Using command = New SqlCommand(sSQL, connection)

        connection.Open()
        Dim p As SqlParameter = command.Parameters.Add("@Output", SqlDbType.VarChar, 255)
        p.Direction = ParameterDirection.InputOutput

        command.ExecuteNonQuery();

        TextBox1.Text = p.Value.ToString()

    End Using
End Using

^{*请原谅任何语法错误，我多年没用过VB.Net了，有些c＃quirks可能在下面，比如我不记得你是不是要用括号对于无参数的方法，或者如果你不能...希望有足够的基本结构来帮助你入门}

SQL查询未在VB.NET中运行

1 个答案: