vb.net - 从 sql 查询中获取单个值到文本框中

Question

我的 sql 查询的结果是一个单一的值，我想在标签中显示它，但不知道如何显示。我有一个创建数据集的解决方案，将查询结果放入该数据集并通过行 (0)、列 (0) 获取它，但我想有一种更聪明的方法。

Private myquery As String

Sub New(ByVal query As String)
    myquery = query
End Sub
Public Sub query_Send()
    Dim myconn As New SqlConnection("Data Source=DB;Integrated Security=TRUE")
    Dim mycmd As SqlCommand = New SqlCommand(Me.myQuery, myconn)
    Dim myTable As New DataTable
    Dim previousConnectionState As ConnectionState = myconn.State
    Try
        If myconn.State = ConnectionState.Closed Then
            myconn.Open()
            Dim myDA As New SqlDataAdapter(mycmd)
            myDA.Fill(myTable)
            tb.text = **...**
        End If
        If previousConnectionState = ConnectionState.Closed Then
            myconn.Close()
        End If
    End Try
End Sub

Answer 1

您可以使用 SqlCommand.ExecuteScalar Method

Dim querystr as String = "select value from MyTable where ID=5"
Dim mycmd As New SqlCommand(querystr, connection)
dim value as Object = mycmd.ExecuteScalar()

您可以放入文本框的值。 ExecuteScalar 返回结果集第一行的第一个值(相当于 row(0).column(0) )当没有记录返回时 value 是 nothing.