如何解决这个Declare变量Sql？

问题描述

我正在制作一个测验应用程序，用户可以在其中编辑数据库中的问题。

我在下面的代码中试图做的是，当用户打开 QuizEditForm，并在显示来自题库的当前数据的 datagridview 中进行更改时，用户可以对其进行编辑，例如添加问题、删除、更新。

当用户进行更改时，我希望将其与他的 UserID 一起插入到数据库中，这样如果多个用户使用该应用程序，他们就只能看到他们的问题。

但是，我一直在尝试在 SQL 语句中修复许多错误，例如声明标量变量、不正确的语法等。有没有人知道如何解决这个问题？

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Quiz_Game_Official
{
    public partial class QuizEditForm : Form
    {
        private string path = Path.Combine(System.IO.Directory.GetCurrentDirectory(),"Database1.mdf");
        private string dbConnectionPath;
        private SqlConnection connectionString;
        private Form mParent;
        public QuizEditForm(Form parent)
        {
            InitializeComponent();
            int UserID = Program.UserID;
       
            
            this.mParent = parent;
            this.dbConnectionPath = String.Format(@"Data Source = (LocalDB)\MSSQLLocalDB; AttachDbFilename = {0}; Integrated Security = True",path);
            this.connectionString = new SqlConnection(dbConnectionPath);

            string SQL = "UPDATE QuestionBank SET UserID = "+UserID +
                "SELECT UserID,QuestionID,QuestionText,CorrectAnswer,WrongAnswer1,WrongAnswer2,WrongAnswer3 FROM QuestionBank";

        //    string SQL = "SELECT UserID,WrongAnswer3 FROM QuestionBank WHERE UserID =" +UserID ; // selecting questions

            SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(SQL,connectionString);
            DataTable quizDataTable = new DataTable();     // prepare datatable to handle data for gridview
            sqlDataAdapter.Fill(quizDataTable);   // sqlDataAdapter respresents question Table
            quizTable.DataSource = quizDataTable;  // datatable is stil data,not UI representaion so we use this line to show it on the UI,this means  table's datasource is quizDataTable variable 
        }

        private void quizTable_CellValueChanged(object sender,DataGridViewCellEventArgs e)   // one of the events,triggered when the user edits cell value
        {
           
            if (quizTable.CurrentRow != null)
            {
                this.connectionString = new SqlConnection(dbConnectionPath);
                using (connectionString)
                {
                    DataGridViewRow quizRow = quizTable.CurrentRow;// this line gets current editing table row
                    int UserID = Program.UserID;
                    string SQL = "DECLARE @QuestionBank TABLE (UserID INT)" +
                        "IF @QuestionID = 0 INSERT INTO QuestionBank(UserID,WrongAnswer3) " +
                                   "OUTPUT INSERTED.UserID INTO @QuestionBank(UserID) VALUES ("+UserID +")"+
                                    "output INSERTED.QuestionID VALUES(@UserID,@QuestionText,@CorrectAnswer,@WrongAnswer1,@WrongAnswer2,@WrongAnswer3)  ELSE " +
                                    "UPDATE QuestionBank SET QuestionText = @QuestionText,CorrectAnswer = @CorrectAnswer,WrongAnswer1 = @WrongAnswer1,WrongAnswer2 = @WrongAnswer2,WrongAnswer3 = @WrongAnswer3,UserID = @UserID " +
                                    "output INSERTED.QuestionID WHERE QuestionID = @QuestionID";  //Question Add or Edit  // update / insert
                    using (SqlCommand command = new SqlCommand(SQL,connectionString)) 
                    {
                        if (quizRow.Cells[0].Value == System.DBNull.Value)  //the select row doesnt have question id meaning it is for new questions
                        {
                            command.Parameters.Add("@QuestionID",SqlDbType.Int).Value = 0;  //  we set question ID to 0 otherwise
                        } 
                        else
                        {
                            command.Parameters.Add("@QuestionID",SqlDbType.Int).Value = quizRow.Cells[0].Value;
                        }
                        
                        command.Parameters.Add("@QuestionText",SqlDbType.VarChar,200).Value = quizRow.Cells[1].Value != System.DBNull.Value ? quizRow.Cells[1].Value : "";
                        command.Parameters.Add("@CorrectAnswer",200).Value = quizRow.Cells[2].Value != System.DBNull.Value ? quizRow.Cells[2].Value : "";
                        command.Parameters.Add("@WrongAnswer1",200).Value = quizRow.Cells[3].Value != System.DBNull.Value ? quizRow.Cells[3].Value : "";
                        command.Parameters.Add("@WrongAnswer2",200).Value = quizRow.Cells[4].Value != System.DBNull.Value ? quizRow.Cells[4].Value : "";
                        command.Parameters.Add("@WrongAnswer3",200).Value = quizRow.Cells[5].Value != System.DBNull.Value ? quizRow.Cells[5].Value : "";

                        try
                        {
                            this.connectionString.Open();
                            int result = (int)command.ExecuteScalar();   //when sql query is ran,it ouputs last inserted or updated id,get the id and store it to results variable
                            int modified = (int)result;
                            UserID = Program.UserID;
                            if (modified == 0)
                            {
                                MessageBox.Show("Quiz Table Update Failed");
                            }
                            quizTable.CurrentRow.Cells[0].Value = modified;                            
                            this.connectionString.Close();
                        }
                        catch (Exception ex)
                        {
                            MessageBox.Show(ex.Message);
                        }
                    }
                }
            }
        }

        private void quizTable_UserDeletingRow(object sender,DataGridViewRowCancelEventArgs e)  // event triggered when user deletes a question 
        {
            //e.Cancel = true;
            if (quizTable.CurrentRow.Cells[0].Value != System.DBNull.Value)
            {
                if (MessageBox.Show("Are you sure to Delete this question?","Warning",MessageBoxButtons.YesNo) == DialogResult.Yes)  // user is asked if he is suere about deleting the question
                {
                    this.connectionString = new SqlConnection(dbConnectionPath);
                    using (connectionString)
                    {
                        DataGridViewRow quizRow = quizTable.CurrentRow;
                        string SQL = "DELETE from QuestionBank WHERE QuestionID = @QuestionID";  //Question Add or Edit
                        using (SqlCommand command = new SqlCommand(SQL,connectionString))
                        {
                            command.Parameters.Add("@QuestionID",SqlDbType.Int).Value = quizRow.Cells[0].Value;
                            try
                            {
                                this.connectionString.Open();
                                int affectedRow = command.ExecuteNonQuery();
                                if (affectedRow == 0)
                                {
                                    e.Cancel = true;
                                    MessageBox.Show("Question delete failed");
                                }
                                this.connectionString.Close();
                            }
                            catch (Exception ex)
                            {
                                e.Cancel = true;
                                MessageBox.Show(ex.Message);
                            }
                        }
                    }
                }
            }
        }

        private void QuizEditForm_FormClosing(object sender,FormClosingEventArgs e)
        {
            this.mParent.Show();
        }
    }
}

解决方法

我不知道从哪里开始。首先，在你做任何事情之前，在 MSDN 上阅读数据库是如何工作的，以及你想要做出的每个语句的正确语法。

我会注意到一些在您的代码中出现的问题，似乎有很多。如果您不清楚其中任何一项，请在理解之前不要继续运行您的应用：

AttachDbFileName 在大多数情况下都是错误的，除了测试。它会创建数据库的副本并在您关闭连接时将其删除。见Bad habits: Using AttachDBFileName
您不应该缓存 SqlConnection 对象，您应该在每次需要时从 连接字符串（它只是一个字符串）创建它。
您应该使用 using 块处理您的连接、命令、适配器和/或读取器对象
我不知道您为什么要以 "UPDATE QuestionBank SET UserID = "+UserID 开始您的主显示，这会将该表中每一行的 UserId 设置为相同。
在 CellValueChanged 中，通常最佳做法是通过 e 参数获取单元格值，而不是仅获取所选行的 CurrentRow，因为它可能已以编程方式更改。
我不完全确定 Upsert（组合插入/更新语句）的意思，但这绝对不是正确的语法，即使是，也不是正确的方法。有关最佳做法，请参阅 here。
如果您要插入一行并且没有 questionID，则需要在插入命令中专门检查。您可以将 if...== System.DBNull.Value 合并为一行：command.Parameters.Add("@QuestionID",SqlDbType.Int).Value = quizRow.Cells[0].Value; 并检查是否为 null。
不要在连接打开时创建 MessageBoxes 或做任何可能需要时间的事情。

c#c#sql sql sql-server-ce

如何解决这个Declare变量Sql？

问题描述

解决方法

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