Thanks for your information.
In fact, the processus is the following : each time I scan a barcode, I
verify that the code isn't present in the table.

The loop in C# is the following :
------------------------------------------------
request = "SELECT CAB_COLIS FROM COLIS WHERE CAB_COLIS='"+code+"'";
if(clsD.searchData(request) == false)
{
// Display the code in a textbox and add the barcode in the table
}
else
{// Display an error message
}
-----------------------------------------------------

Where the searchData function is the following :
---------------------------------------------------------
public bool searchData(string req)
{
bool status = false;
SqlCeConnection connDB = new SqlCeConnection(strConn);       
SqlCeCommand cmndDB = new SqlCeCommand(req, connDB);
SqlCeDataReader drdrDB;               

try
{
connDB.Open();
drdrDB = cmndDB.ExecuteReader();           

while ( drdrDB.Read() )
{
status = true;               
}
               
drdrDB.Close();

connDB.Close();
}
catch(Exception ex)
{
MessageBox.Show(ex.ToString(),
"Erreur",                System.Windows.Forms.MessageBoxButtons.OK,System.Windows.Forms.MessageBoxIcon.Hand,System.Windows.Forms.MessageBoxDefaultButton.Button2);
}
return status;
}
---------------------------------------------------------------------------

So, I open each time the connection to the database and I make a request
including the primary key in the where clause.

Thanks for any suggestion.