Question

我正在尝试用VB创建一个库管理系统（Visual Basic 2010）。

我有一个名为DataGridViewLoans的DataGridView，用于显示读者的当前贷款。它与主窗口分开，当表单加载时，读者ID将传递给表单。

我希望它（DataGridViewLoans）显示当前为读者提供的贷款，书籍标题。

我在Access中创建了一个SQL查询，并将其包含在代码中。但是，当我运行程序时，它说：没有给出一个或多个必需参数的值。

我尝试了各种不同的方法，但总是会出现同样的错误。

程序在＆＃34; dAdapter.Fill（dataTable）＆＃34;上给出了错误。线。

这是我的代码：

Dim connectionString As String = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = C:\Documents and Settings\Timothy\My Documents\Visual Studio 2010\Projects\LibraryManagementSystemPrototype\Database\library.mdb;"
    Dim query As String = "SELECT Catalogue.Number, Catalogue.Title, Catalogue.Author, Catalogue.ID, Loans.[Issue Date], Loans.[Date Due], Loans.Overdue, Loans.[Days Overdue], Loans.ID_ENROLMENT, Loans.ID_CATALOGUE FROM Catalogue INNER JOIN Loans ON Catalogue.ID = Loans.ID_CATALOGUE WHERE (((Catalogue.ID)=[Loans].[ID_CATALOGUE]) AND ((Loans.ID_ENROLMENT)=[Enrolment].[ID]));"

    Dim dAdapter As OleDb.OleDbDataAdapter = New OleDb.OleDbDataAdapter(query, connectionString)
    Dim cBuilder As OleDb.OleDbCommandBuilder = New OleDb.OleDbCommandBuilder(dAdapter)

    Dim dataTable As New DataTable()

    dAdapter.Fill(dataTable)

    Dim bindingSource As New BindingSource()
    bindingSource.DataSource = dataTable

    DataGridViewLoans.DataSource = bindingSource

谁能告诉我我做错了什么？

由于

Answer 1

通常，当您的字段或表名中有一个或多个拼写错误时会发生这种情况，但在这种情况下，您完全错过了Enrollment表上的联接。你可以在FROM / JOIN部分的任何地方使用它

Dim query As String = "SELECT Catalogue.Number, Catalogue.Title, " & _ 
   "Catalogue.Author, Catalogue.ID, Loans.[Issue Date], Loans.[Date Due], " & _ 
   "Loans.Overdue, Loans.[Days Overdue], Loans.ID_ENROLMENT, Loans.ID_CATALOGUE " & _
   "FROM Catalogue INNER JOIN Loans ON Catalogue.ID = Loans.ID_CATALOGUE " & _
   "INNER JOIN Enrolment ON Enrolment.ID = Loans.ID_Enrolment"

如您所见，WHERE部分是不必要的

VB.Net：没有给出一个或多个必需参数的值

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