如何將MySql選擇轉換爲字符串？

Question

我有一個帶有MySql數據庫的ASP.NET C＃中製作的webform。數據庫包含一個名爲id的字段，它是主要的，自動遞增的和INT類型的。

我想選擇一個特定的記錄，比如數字10，將它轉換爲一個字符串，這樣我就可以將它與另一個字符串進行比較。

編輯，在全碼：

public partial class index : System.Web.UI.Page 
{ 
    // ConnString 

    String SqlConnString; 
    String qs; 

    private MySqlCommand SqlCommand; 
    private MySqlConnection dbConnection; 

    protected void btnSubmit_Click(object sender, ImageClickEventArgs e) 
    { 
     if (Page.IsValid) 
     { 
      // Variabele 

      string textbox = tbTextbox.Text; 


      // DbConnection 
      SqlConnString = ConfigurationManager.ConnectionStrings["ConnString"].ConnectionString.ToString(); 

      SqlCommand = new MySqlCommand(); 
      dbConnection = new MySqlConnection(); 
      dbConnection.ConnectionString = SqlConnString; 

      // qs 
      qs = "INSERT INTO applys" + 

       "(textbox, date)" + 

       " VALUES (@textbox, NOW())"; 

      // Parameters 
      SqlCommand.Parameters.Clear(); 
      SqlCommand.Parameters.AddWithValue("@textbox", date); 

      //open database 
      dbConnection.Open(); 
      SqlCommand.CommandText = qs; 
      SqlCommand.Connection = dbConnection; 

      SqlCommand.ExecuteNonQuery(); 

      SqlCommand.Dispose(); 

      dbConnection.Dispose(); 

      /////////// 

      MySqlDataReader reader = null; 
      MySqlConnection con = null; 
      MySqlCommand cmd = null; 
      //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
      string ConnectionString = "connection string"; 
      con = new MySqlConnection(ConnectionString); 
      string query = "SELECT id FROM apply WHERE id = 10"; 
      cmd = new MySqlCommand(query); 
      cmd.Connection = con; 

      try 
      { 
       // Open Connection 
       con.Open(); 

       // Execute the query 
       reader = cmd.ExecuteReader(); 

       bool found = false; 
       while (reader.Read()) 
       { 
        if (reader["id"].ToString() == "10") 
        { 
         found = true; 
         break; 
        } 
       } 
       if (found) 
       { 
        ltl.Text = "Worked!"; 
        //Response.Redirect("different page"); 
       } 
       else 

        ltl.Text = "Nope"; 
        //Response.Write("Nothing!"); 

      } 
      catch 
      {     
       // MessageBox.Show("Error!"); 
      } 

      int id = -1; 
      id = (Int32)cmd.ExecuteScalar(); 
      if (id != -1) 

       ltl.Text = "Worked!"; 
       //Response.Redirect("different page"); 

      reader.Dispose(); 
      reader.Close(); 
      con.Dispose(); 
      con.Close(); 
      cmd.Connection.Close(); 
      cmd.Dispose(); 


     } 
    } 
} 

Answer 1

var query = "SELECT id FROM applys WHERE id = 10"; 
var connectionString = "yourmysqlconnectionstringgoeshere"; 
using(var connection=new MySqlConnection(connectionString)) 
{ 
    connection.Open(); 
    using (var reader = new MySqlCommand(query, connection).ExecuteReader()) 
    { 
     if(reader.Read()) 
     { 
      if (reader["id"].ToString() =="10") 
      { 
       // do your stuff here 
      } 
     } 
    } 
} 

Answer 2

你必須這樣做仔細的步驟：

SqlDataReader rdr = null; 
SqlConnection con = null; 
SqlCommand cmd = null; 
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
string ConnectionString = "server=.;uid=sa; pwd=123; database=MyDB"; 
con = new SqlConnection(ConnectionString); 
string query = "SELECT id FROM applys WHERE id = 10"; 
cmd = new SqlCommand(query); 
cmd.Connection = con; 

try 
{ 
    // Open Connection 
    con.Open(); 

    // Execute the query 
    reader = cmd.ExecuteReader(); 

    bool found=false; 
    while(reader.Read()) 
    { 
     if (reader["UserName"].ToString()=="Ram") 
     { 
      found=true; 
      break; 
     } 
    } 
    if (found) 
    { 
     Response.Redirect("different page"); 
    } 

    else 
     Response.Write("Nothing!"); 
} 
catch{ 
    MessageBox.Show("Error!"); 
} 

另外，在你的情況下，你可以使用ExecuteScalar()。它將在第一行，第一列從SELECT語句返回一個值：

int id=-1; 
id=(Int32)cmd.ExecuteScalar(); 
if (id!=-1) 
    Response.Redirect("different page");