尝试从 Access 数据库中搜索时出现 C# OleDb 异常“没有为一个或多个必需参数提供值”

如何解决尝试从 Access 数据库中搜索时出现 C# OleDb 异常“没有为一个或多个必需参数提供值”

我正在尝试使用 Windows 窗体应用程序在 Access 数据库上搜索输入值，找到的结果应显示在文本框中。但我不断收到此错误。

这是我的代码：

private void btn_search_Click(object sender,EventArgs e)
       {
            string search = "";
            SearchForm popup = new SearchForm();
            DialogResult dialogresult = popup.ShowDialog();
            if (dialogresult == DialogResult.OK)
            {
                search = SearchForm.item;
                
                if (search != "")
                {
                    Access_Connections.sql = "SELECT * FROM Learners WHERE @val IN(ID,Learner_name,Learner_surname,Grade,School,Gender,Blood_group,Home_language,Church_relation,Hostel_block);";

                    Access_Connections.cmd.Parameters.AddWithValue("@val",search);

                    Access_Connections.cmd.Parameters.Clear();
                    Access_Connections.cmd.CommandType = CommandType.Text;
                    Access_Connections.cmd.CommandText = Access_Connections.sql;
                    Access_Connections.cmd.Connection = Access_Connections.con;

                    Access_Connections.openConnection();

                    Access_Connections.rd = Access_Connections.cmd.ExecuteReader();

                    while (Access_Connections.rd.Read())
                    {
                        text_name.Text += Access_Connections.rd["Learner_name"].ToString();
                        text_surname.Text += Access_Connections.rd["Learner_surname"].ToString();
                        text_grade.Text += Access_Connections.rd["Grade"].ToString();
                        text_school.Text += Access_Connections.rd["School"].ToString();

                    }

                    Access_Connections.closeConnection();
                }
                else if (dialogresult == DialogResult.Cancel)
                {
                    Console.WriteLine("You clicked either Cancel or X button in the top right corner");
                }
                popup.dispose();
            }
        } 

解决方法

你把它颠倒过来了：

"SELECT * FROM Learners WHERE (Learner_name=@val OR Learner_surname=@val OR Grade=@val OR School=@val OR Gender=@val OR Blood_group=@val OR Home_language=@val OR Church_relation=@val OR Hostel_block=@val);"