OLEDB 命令中忽略的最后一个 'OR' 语句

Question

我试图通过在单个数据库字段上使用多个 'OR' 语句来过滤 OLEDB 命令，但链中的最后一个语句被忽略并且没有 return 任何东西。

我现在有一个解决方法，@null 请求 returns "DBNull.value" 但是如果我从下面删除“[doctype] = @null”，它会忽略“[doctype] =文档类型 3"

& "WHERE [doctype] = @doctype OR [doctype] = @doctype2 OR [doctype] = @doctype3 OR [doctype] = @null " _

我可以根据需要增加或减少 'OR Statements'，但总是忽略最后一个 'OR Statement'。

我试过将 'OR statements' 放在方括号中，但 return 什么都没有，或者我做错了。

我正在寻找为什么最后一个 'or statement' 在 oledbcommand 字符串中被忽略，但如果你能改进我写的任何代码，请做，但向我解释 why/how。

它们的使用位置（每个其他值都有 DBNull.value 用于测试目的）

            f_doctype = "MS"
            f_doctype2 = "TMS"
            f_doctype3 = "CS"

            With cmdaRefresh.Parameters
            .AddWithValue("doctype", CType(f_doctype, String))
            .AddWithValue("doctype2", CType(f_doctype2, String))
            .AddWithValue("doctype3", CType(f_doctype3, String))
            .AddWithValue("null", DBNull.Value)
            .AddWithValue("docnum", DBNull.Value)
            .AddWithValue("docrev", DBNull.Value)
            .AddWithValue("matname", DBNull.Value)
            .AddWithValue("status", DBNull.Value)
            .AddWithValue("actionreq", DBNull.Value)
            .AddWithValue("createdby", DBNull.Value)
            .AddWithValue("createddate", DBNull.Value)
            .AddWithValue("finalby", DBNull.Value)
            .AddWithValue("finaldate", DBNull.Value)
            End With

        Dim cmdRefresh As New OleDbDataAdapter(cmdaRefresh)

        'open connection
        myconnection.Open()

        'read and fill dataset for gridview
        cmdRefresh.Fill(dsRefresh, tbl_string.tablename)

        'close connection
        myconnection.Close()

'fill datagrid with values from database and alter column headers to match criteria
        With dg_speclog
            .DataSource = dsRefresh.Tables(0)
            .RowHeadersVisible = False
            .Columns(0).HeaderCell.Value = "Category"
            ...
        End With

完整'oledbcommand'创作

Dim cmdaRefresh As OleDbCommand = New OleDbCommand(" SELECT [doctype], [docnum], [docrev], [matname], [status], [actionreq], [createdby], [createddate], [finalby], [finaldate] " _
                                                              & "FROM " & tbl_string.tablename & " " _
                                                              & "WHERE [doctype] = @doctype OR [doctype] = @doctype2 OR [doctype] = @doctype3 OR [doctype] = @null " _
                                                              & "AND [docnum] = @docnum " _
                                                              & "AND [docrev] = @docrev " _
                                                              & "AND [matname] = @matname " _
                                                              & "AND [status] = @status " _
                                                              & "AND [actionreq] = @actionreq " _
                                                              & "AND [createdby] = @createdby " _
                                                              & "AND [createddate] = @createddate " _
                                                              & "AND [finalby] = @finalby " _
                                                              & "AND [finaldate] = @finaldate " _
                                                              & "ORDER BY [docnum] ASC, [docrev] ASC " _
                                                              , myconnection)

Answer 1

您需要使用 IS NULL 来检查空值（在大多数（也许是所有）数据库中，空值不等于空值，因此您需要改用 IS 运算符）。这也意味着您不需要所有这些参数。

根据您打算如何将 [doctype] IS NULL 检查与其他空检查结合起来，您可能还需要将 OR 括在括号中, 因为 AND 的优先级可能高于 OR.

Dim cmdaRefresh As OleDbCommand = New OleDbCommand(
    " SELECT [doctype], [docnum], [docrev], [matname], [status], [actionreq], [createdby], [createddate], [finalby], [finaldate] " _
    & "FROM " & tbl_string.tablename & " " _
    & "WHERE ([doctype] = @doctype OR [doctype] = @doctype2 OR [doctype] = @doctype3 OR [doctype] IS NULL) " _
    & "AND [docnum] IS NULL " _
    & "AND [docrev] IS NULL " _
    & "AND [matname] IS NULL " _
    & "AND [status] IS NULL " _
    & "AND [actionreq] IS NULL " _
    & "AND [createdby] IS NULL " _
    & "AND [createddate] IS NULL " _
    & "AND [finalby] IS NULL " _
    & "AND [finaldate] IS NULL " _
    & "ORDER BY [docnum] ASC, [docrev] ASC " _
    , myconnection)

如果[doctype] IS NULL支票与其他NULL支票属于同一支票，则您不需要括号。

Answer 2

已找到无法正常工作的原因。在我搜索的某个地方，我读到 DBNull.value 与 .addwithvalue 语句一起使用时会 return 数据库中的任何内容（这可能会混淆整个事情）。这是不正确的，它 return 是 no white space or value 中任何具有 nothing 值的东西。这就是为什么 [doctype] IS NULL 给出了与上面相同的问题，我认为它做同样的事情。

我一直在寻找一种方法来搜索我的 [doctype] 和 return 其他数据库字段中的任何值，而无需指定任何内容 'for testing'

我正在寻找的语句是 [docnum] LIKE '%' 这称为通配符。通配符可用于替换字符串中的任何其他字符，因此这意味着任何内容都是 returned。但是，如果数据库字段的值为 Null，则仍然需要 IS NULL 语句，因此我在下面进行了 [finalyby] & [finaldate] 更改。

我现在想到的是：

'CHANGED (dataadapter > command)
    Dim cmdaRefresh As OleDbCommand = New OleDbCommand(" SELECT [doctype], [docnum], [docrev], [matname], [status], [actionreq], [createdby], [createddate], [finalby], [finaldate] " _
                                                              & "FROM " & tbl_string.tablename & " " _
                                                              & "WHERE [doctype] IN (@doctype, @doctype2 ,@doctype3) " _
                                                              & "AND [docnum] LIKE '%' " _
                                                              & "AND [docrev] LIKE '%' " _
                                                              & "AND [matname] LIKE '%' " _
                                                              & "AND [status] LIKE '%' " _
                                                              & "AND [actionreq] LIKE '%' " _
                                                              & "AND [createdby] LIKE '%' " _
                                                              & "AND [createddate] LIKE '%' " _
                                                              & "AND ([finalby] LIKE '%' OR [finalby] IS NULL) " _
                                                              & "AND ([finaldate] LIKE '%' OR [finaldate] IS NULL) " _
                                                              & "ORDER BY [docnum] ASC, [docrev] ASC " _
                                                              , myconnection)

感谢帮助过的人

OLEDB 命令中忽略的最后一个 'OR' 语句

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