如何解决如何解决这个Declare变量Sql？
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。
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