数据存在，但是我的程序说“行/列没有数据”。

Question

    private void recordFromTable()
    {
        String firstName = Environment.UserName.Split('.')[0];
        String lastName = Environment.UserName.Split('.')[1];
        String query = "SELECT LastUpdate FROM " + "EmployeeContact" + " WHERE EmployeeLastName='" + lastName + "' AND EmployeeFirstName='" + firstName + "'";
        try
        {
            using (OleDbConnection connection = new OleDbConnection(connectionString))
            {
                OleDbCommand command = new OleDbCommand(query, connection);
                connection.Open();
                using (OleDbDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        labelLastUpdated.Text = reader.GetString(0).Trim();
                    }
                }
            }
        } catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }

引发的异常是行/列中没有数据。

我打开Access数据库并运行相同的查询（检查员在调试时显示的查询），并从数据库返回了一行。

Access中的所有字段均为“短文本”

Answer 1

很可能没有记录满足指定的WHERE条件，因此没有上述记录。 要验证运行此

SELECT COUNT(*) FROM 
EmployeeContact 
WHERE EmployeeLastName= lastName 
AND EmployeeFirstName=firstName;

您可能还想将查询更改为此

String query = "SELECT Nz(LastUpdate, 'NO DATA PRESENT') LastUpdate FROM " + "EmployeeContact" + " WHERE EmployeeLastName='" + lastName + "' AND EmployeeFirstName='" + firstName + "'";

Answer 2

如果您确定数据存在，在我看来，您的firstName或lastName变量可能没有被分配您认为是或希望它们的值。