无法将vb.net项与访问号进行比较

Question

Edit: For anyone facing this problem, don't miss the tips about only using parameters instead of inserting the values directly into the SQL queries.

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i'm facing a big problem with my vb.net project, i'm stuck with this for a week

i've a combobox item that i need to compare with an access number which is my database to retrieve some information, but i just got an error, no matter what format i convert my combobox item, it says my datatype is inconpatible with the expression

Here's one of the SQL queries from my code:

Dim dt1 As New DataTable 

'This query select some itens from a row that match with the selected combobox number  

Dim find1 As New OleDb.OleDbDataAdapter("SELECT Product, Number," _ 
& " Customer, Quantity, ProductionDate, AskDay, Pack, Company FROM RegOPE" _ 
& " WHERE Number ='" & CInt(mycombobox.SelectedItem) & "'", cn)

'Ive tried SelectedItem, Item, Text, SelectedValue...  
'For conversion i tried parse, tryparse, conversion...  

cn.Open() 'Opens database connection  
find1.Fill(dt1)  <- I got the error here  
cn.Close() 'Close database connect  
mydatagrid.DataSource = dt1 'Show the result in datagridview  

Answer 1

In your WHERE clause have you tried to remove the quotes ? They are not required if you are looking for a number.

Answer 2

number criteria should be without quote

Dim find1 As New OleDb.OleDbDataAdapter("SELECT Product, Number, " _
                                      & "Customer, Quantity, ProductionDate, AskDay, Pack, Company FROM RegOPE " _
                                      & "WHERE Number =" & CInt(mycombobox.SelectedItem), cn)

But better always use parameters:

Dim comm = New OleDb.OleDbCommand("SELECT Product, Number, " _
                                      & "Customer, Quantity, ProductionDate, AskDay, Pack, Company FROM RegOPE " _
                                      & "WHERE Number =?", cn)

comm.Parameters.AddWithValue("unusedName", mycombobox.SelectedItem)

Dim find1 As New OleDb.OleDbDataAdapter(comm)

Answer 3

First, I must mention that you really ought to be using parameters. You should not concatenate the values directly into the SQL command string like that. Your SQL command string should simply contain parameter name placeholders for those values and then you should specify the values for those parameters separately.

However, if you are going to concatenate the value with the command like that, the command is a string, not an integer. It makes little sense to use CInt to convert the item to an integer just before concatenating it with a string (which requires first converting it from the integer into a string). It would make more sense to simply call ToString to convert it to a string, instead of CInt . Also, if the Number column in your database is typed as a number, rather than as text, then you should not be surrounding the value with quotes.

I recommend trying this:

Dim find1 As New OleDb.OleDbDataAdapter("SELECT Product, Number," _ 
    & " Customer, Quantity, ProductionDate, AskDay, Pack, Company FROM RegOPE" _ 
    & " WHERE Number =" & mycombobox.SelectedItem.ToString(), cn)

Although, recommend is to strong a word, since I would never recommend doing it that way in the first place. Use parameterized queries!