Question

我需要选择最小自动增量编号，然后在选择学生信息时选择ID编号作为参考。这就是我所拥有的：

strSQL = "SELECT min(number) from main_queue "
cmd = New MySqlCommand(strSQL, CONNECTION)
dr = cmd.ExecuteReader
If dr.HasRows Then
    dr.Read()
    Dim min As Integer
    min = dr("min(number)")
    strSQL = "SELECT idno_ from main_queue where number='" + min + "'"
    cmd = New MySqlCommand(strSQL, CONNECTION)
    If dr.HasRows Then
        dr.Read()
        Dim idnum As Integer
        idnum = dr("idno_")
        strSQL = "SELECT * from student_records where number='" + idnum + "'"
        cmd = New MySqlCommand(strSQL, CONNECTION)
        If dr.HasRows Then
            dr.Read()
            mon_name.Text = dr("name_")
            mon_IDno.Text = dr("IDno")
        End If
    End If
End If

我收到“从字符串转换”“到'Double'类型无效。”行中的错误，我使用最小自动增量编号作为参考选择id号。

Answer 1

也许我对您的数据库架构没有正确理解，但似乎您可以在一个查询中全部编写

Dim strSQL = "SELECT * FROM student_records " & _
             "where idNO =  " & _
             "(SELECT idno_ from main_queue where number= " & _
             "(SELECT min(number) from main_queue))"
cmd = New MySqlCommand(strSQL, CONNECTION)
If dr.Read() Then
    mon_name.Text = dr("name_")
    mon_IDno.Text = dr("IDno")
End If

Answer 2

设法让它发挥作用！这是我的代码

SELECT * from student_records where IDno in (select idno_ from main_queue where number in (SELECT min(number) as min_number from main_queue))

错误：从字符串“”到“Double”类型的转换无效

2 个答案: