空单元格查询仅适用于 "LEN(name) > 1 or LEN(name) < 2"

Question

在我的程序 (vb.net) 中，当我使用“LEN(EnterName) > 1 or LEN(EnterName) < 2”，这很奇怪，因为 > 1 和 <2 只会 select 任何单元格，就像没有 LEN 一样。

如果我不使用 LEN，则会收到此错误消息

"The given transformation is invalid"

这不是唯一的问题。当我使用 LEN 时，它不会 return 我需要的空单元格。

如果你能帮助我，那就太好了。

Picture of Database and vb Application (using LEN) 对不起，为了数据保护，我需要对除这一行以外的任何内容进行像素化。如果您需要更多信息，请问我！

代码：

    Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\temp\WE2015_NEU dura logo.mdb;Persist Security Info=False;")

        'fills the combobox with information from the database
        '═══════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╗
        connection.Open()                                                                                                                      '║
        Dim command_Name_Firmen As New OleDbCommand("SELECT Betrieb FROM MaterialHist Where LEN(Betrieb) > 1 or LEN(Betrieb) < 2", connection) '║
        Dim reader_Name_Firmen As OleDbDataReader = command_Name_Firmen.ExecuteReader()                                                        '║
        While reader_Name_Firmen.Read()                                                                                                        '║
            DatenbankboxDrölf.Items.Add(reader_Name_Firmen.GetString(0))   ''Here in the Brackets is the error if i would not use LEN          '║(Datenbankdrölf = Combobox)
        End While                                                                                                                              '║
        reader_Name_Firmen.Close()                                                                                                             '║
        connection.Close()                                                                                                                     '║
        '═══════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════╝

    End Using

Answer 1

您似乎需要正确处理 NULL 值，使用 IsDbNull()

见vb.net - read null value from database

空单元格查询仅适用于 "LEN(name) > 1 or LEN(name) < 2"

Query with empty cells only works with "LEN(name) > 1 or LEN(name) < 2"

vb.net

oledb

ms-access-2000