选择 Max Visual Studio 2010

Question

我正在将一个程序从 Visual Basic 6 更新到 Visual Studio 2010，当然，我发现了很多问题，所以请解决。

我正在使用具有相同键（索引）的四个表的 Access 数据库。

如果我使用如下代码，我可以从 CodDekafix 表中获取最后一条记录：

Private Sub cmdLast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles   cmdLast.Click
    Dim Con As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\DEKAFIX\Consulta Dekafix\dekafix.mdb")
    Dim cmd As New OleDbCommand()
    Con.Open()
    sql = "Select * From Indice Where CodDekafix=(Select max(CodDekafix) From Indice)"

但是，如果我想从具有相同键（索引）的所有表中获取所有结果，并进行如下所示的更改，则程序不起作用。

sql = "Select * from Indice, dekafix1, dekafix2, dekafix3" _
      & " where CodDekafix=(Select max(CodDekafix) From Indice) and" _
      & " Indice.CodDekafix = dekafix1.CodDekafix and" _
      & " dekafix1.CodDekafix=dekafix2.CodDekafix and" _
      & " dekafix2.CodDekafix=dekafix3.CodDekafix and" _
      & " ORDER BY Indice.CodDekafix"

Answer 1

您在第二个代码示例中的 SQL 代码无效。当我们在 VB 代码中去掉表示字符串的格式时，你会得到：

Select * from Indice, dekafix1, dekafix2, dekafix3
where CodDekafix=(Select max(CodDekafix) From Indice) and
Indice.CodDekafix = dekafix1.CodDekafix and
dekafix1.CodDekafix=dekafix2.CodDekafix and
dekafix2.CodDekafix=dekafix3.CodDekafix and
ORDER BY Indice.CodDekafix

这里有两个问题：

1) 在 ORDER BY 子句之前有一个额外的“and”。删除它。

2) WHERE 子句的第一行对 CodDekafix -- 您需要指定来自哪个表。 将 CodDekafix 替换为 Indice.CodDekafix 应该可以解决问题。

sql = "Select * from Indice, dekafix1, dekafix2, dekafix3" _
  & " where Indice.CodDekafix=(Select max(CodDekafix) From Indice) and" _
  & " Indice.CodDekafix = dekafix1.CodDekafix and" _
  & " dekafix1.CodDekafix=dekafix2.CodDekafix and" _
  & " dekafix2.CodDekafix=dekafix3.CodDekafix" _
  & " ORDER BY Indice.CodDekafix"