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”[关闭]

Posted 2023-04-12

【中文标题】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”[关闭]

【英文标题】：C# OleDb Exception “No value given for one or more required parameters” while trying to search from Access database [closed]

【发布时间】：2021-05-28 01:22:44

【问题描述】：

我正在尝试使用 Windows 窗体应用程序在 Access 数据库中搜索输入值，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();
            
         

【问题讨论】：

你添加参数，然后立即清除参数...

您的连接字符串有问题。

另外：如果抛出异常，closeConnection() 函数将不会运行，从而使数据库文件锁定打开。将连接放在using 块内！

【参考方案1】：

你把它颠倒了：

"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);"