查看在VB利用訪問數據庫中的數據圖表

Question

我要查看該數據的圖表在我的數據庫 我想這個代碼，但我得到一個錯誤信息

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 

    Chart1.Series.Add("Total number of Orders for each Company") 

    Dim Conn As OleDbConnection = New OleDbConnection 
    Dim provider = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source =" 
    Dim dataFile = "F:\College Files\Co-op Files\Aramco Project\Application\OrdersApplication\OrdersApplication\Database.accdb" 
    Conn.ConnectionString = provider & dataFile 
    Conn.Open() 

    Dim cmd As OleDbCommand = New OleDbCommand("SELECT [CompanyID], (SELECT COUNT(QuantityRequired) FROM Order_Details) FROM [Orders] ", Conn) 
    Dim dr As OleDbDataReader = cmd.ExecuteReader 
    While dr.Read 
     Chart1.Series("Total number of Orders for each Company").Points.AddY(dr("CompanyID").ToString, dr("QuantityRequired").ToString) 
    End While 
    dr.Close() 
    cmd.Dispose() 

End Sub 

錯誤消息說QuantityRequired在此行的附加信息

 Chart1.Series("Total number of Orders for each Company").Points.AddY(dr("CompanyID").ToString, dr("QuantityRequired").ToString) 

當我刪除指望它顯示出來，但我需要它來計算每家公司ID

Answer 1

你錯過了阿里所需數量作爲給出的字段名稱：

Dim cmd As OleDbCommand = New OleDbCommand("SELECT [CompanyID], (SELECT COUNT(*) FROM Order_Details) As QuantityRequired FROM [Orders] ", Conn) 

只是猜測。 SQL閱讀：

"SELECT [CompanyID], (SELECT COUNT(*) FROM Order_Details AS T WHERE T.OrderId = Orders.Id) As QuantityRequired FROM [Orders]"