如何在vb.net中使用数据读取器从多个表中读取数据？

以下是我的代码，我无法执行数据读取器，它不断显示错误，因为已经有一个打开的数据读取器与此命令关联，必须先关闭。因此，是否有人可以帮助解决我代码的错误

    Dim selectSql As String
    Dim selectSql2 As String

    conn = New SqlConnection("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Assignment.mdf;Integrated Security=True;Connect Timeout=30")

    selectSql = "Select [Field of Study Deg], [Major Deg], [Institute Or University Deg], [Grade Deg],[Graduation Date Deg], [Field of Study Dip], [Major Dip], [Institute Or University Dip], [Grade Dip], [Graduation Date Dip] From [Education Background] Where [Full Name] = @fullname"

    selectSql2 = "Select [Company Name 1], [Position Title 1], [Position Level 1], [Specialization 1], [Industry 1], [Duration 1], [Work Description 1], [Company Name 2], [Position Title 2], [Position Level 2], [Specialization 2], [Industry 2], [Duration 2], [Work Description 2] From [Employment History] Where [Full Name] = @fullname"

    conn.Open()

    'create the command 
    'the command is used for executing the SQL statement
    cmd = New SqlCommand(selectSql, conn)
    cmd.Parameters.AddWithValue("@fullname", txtFullname.Text)
    dr = cmd.ExecuteReader() 'executes the reader to read record

    cmd2 = New SqlCommand(selectSql2, conn)
    cmd2.Parameters.AddWithValue("@fullname", txtFullname.Text)
    dr2 = cmd2.ExecuteReader()

    If dr.HasRows And dr2.HasRows Then
        btnEdit.Enabled = True
        btnBrowse.Enabled = True

        'read the data from the record 
        dr.Read()
        dr2.Read()

        'display 
        txtField1.Text = dr("Field of Study Deg").ToString
        txtMajor1.Text = dr("Major Deg").ToString
        txtInstitute1.Text = dr("Institute Or University Deg").ToString
        txtGrade1.Text = dr("Grade Deg").ToString
        mskGradDate1.Text = dr("Graduation Date Deg").ToString

        txtCompany1.Text = dr2("Company Name 1").ToString
        txtPosTitle1.Text = dr2("Position Title 1").ToString
        txtPosLevel1.Text = dr2("Position Level 1").ToString
        txtSpecial1.Text = dr2("Specialization 1").ToString
        txtIndustry1.Text = dr2("Industry 1").ToString
        txtDuration1.Text = dr2("Duration 1").ToString
        txtWork1.Text = dr2("Work Description 1").ToString

    Else
        'record not found
        MessageBox.Show("Full name cannot be found. Please check the name again.", "Unable to Search", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
    End If
    conn.Close()
End Sub

---

大多数数据库对象都需要关闭并释放（调用了它们的

.Dispose

方法）

使用…End-Using

块，即使出现错误，也要为您解决这个问题

对于Sql Server，请使用参数的

.Add

方法。看见 和 还有一个： 这是另一个

请注意，在创建第二个读卡器之前，第一个读卡器由

端关闭并使用

处理。这两个命令的连接都保持打开状态

我真的不喜欢在连接打开时更新用户界面，但我们将把它留到下一次

Private Sub OPCode()
    Dim selectSql = "Select [Field of Study Deg], [Major Deg], [Institute Or University Deg], [Grade Deg],[Graduation Date Deg], [Field of Study Dip], [Major Dip], [Institute Or University Dip], [Grade Dip], [Graduation Date Dip] From [Education Background] Where [Full Name] = @fullname"
    Dim selectSql2 = "Select [Company Name 1], [Position Title 1], [Position Level 1], [Specialization 1], [Industry 1], [Duration 1], [Work Description 1], [Company Name 2], [Position Title 2], [Position Level 2], [Specialization 2], [Industry 2], [Duration 2], [Work Description 2] From [Employment History] Where [Full Name] = @fullname"

    Using conn = New SqlConnection("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\Assignment.mdf;Integrated Security=True;Connect Timeout=30")
        Using cmd As New SqlCommand(selectSql, conn)
            cmd.Parameters.Add("@fullname", SqlDbType.VarChar, 200).Value = txtFullname.Text
            conn.Open()
            Using dr = cmd.ExecuteReader
                dr.Read()
                txtField1.Text = dr("Field of Study Deg").ToString
                txtMajor1.Text = dr("Major Deg").ToString
                txtInstitute1.Text = dr("Institute Or University Deg").ToString
                txtGrade1.Text = dr("Grade Deg").ToString
                mskGradDate1.Text = dr("Graduation Date Deg").ToString
            End Using
        End Using
        Using cmd2 As New SqlCommand(selectSql2, conn)
            cmd2.Parameters.Add("@fullname", SqlDbType.VarChar, 200).Value = txtFullname.Text
            Using dr2 = cmd2.ExecuteReader
                dr2.Read()
                txtCompany1.Text = dr2("Company Name 1").ToString
                txtPosTitle1.Text = dr2("Position Title 1").ToString
                txtPosLevel1.Text = dr2("Position Level 1").ToString
                txtSpecial1.Text = dr2("Specialization 1").ToString
                txtIndustry1.Text = dr2("Industry 1").ToString
                txtDuration1.Text = dr2("Duration 1").ToString
                txtWork1.Text = dr2("Work Description 1").ToString
            End Using
        End Using
    End Using
End Sub

---

建议，为什么不在sql字符串中使用

internal JOIN

，将两个表中的连接值合并到一个

SqlDataReader

。例如：

在[Education Background].[Full Name]=[Employment History].[Full Name]上的[Education Background]内部加入[Employment History]，其中[Full Name]=@fullname那么你不需要单独处理每个读者。这是否回答了你的问题。这与您的问题不完全相同，但问题本身显示了一种方式，它正在为旧系统寻找替代方案。很抱歉，我对vb.net还是很陌生，因此对于内部连接，只是select语句不同，而其他代码保持不变？或者你能帮我修改代码吗，谢谢
internaljoin
是
sql查询
，没有任何与
vb.net
相关的内容。根据prev.comment中提供的建议，您不再需要
cmd2
和
dr2
，所有内容都在
dr
中。如果我想从combobox中读取数据，如何检索数据，因为我尝试使用这些代码，但失败了。cboProficiency.Text=dr（“熟练程度”）。ToStringI在您的原始代码中没有看到cboProficiency。是，我没有在我的原始代码中添加该选项，但现在我想在组合框中检索数据。这是一个已经包含项目的现有组合框吗？是的，组合框包含项目，但我想读取数据并在其中显示，同时更新它。