c# - 在 asp.net 中的标签中显示 SQL 查询结果

Question

我正在尝试在标签中显示 SQL 查询结果，但它没有显示。这是我的代码：

     string result = "SELECT ACTIVE FROM [dbo].[test] WHERE ID = '" + ID.Text + "' ";
     SqlCommand showresult = new SqlCommand(result, conn);
     conn.Open();
     showresult.ExecuteNonQuery();
     string actresult = ((string)showresult.ExecuteScalar());
     ResultLabel.Text = actresult;
     conn.Close();

请需要帮助。谢谢！

Answer 1

试试这个。

   string result = "SELECT ACTIVE FROM [dbo].[test] WHERE ID = '" + ID.Text + "' ";
   SqlCommand showresult = new SqlCommand(result, conn);
   conn.Open();
   ResultLabel.Text = showresult.ExecuteScalar().ToString();
   conn.Close();

Answer 2

using (SqlConnection conn = new SqlConnection(connectionString))
{
    string result = "SELECT ACTIVE FROM [dbo].[test] WHERE ID = @id";
    SqlCommand showresult = new SqlCommand(result, conn);
    showresult.Parameters.AddWithValue("id", ID.Text);

    conn.Open();
    ResultLabel.Text = showresult.ExecuteScalar().ToString();
    conn.Close();
}

这将处理连接并且在查询中没有字符串连接。

Answer 3

里面有错别字吗？您对数据库有两次调用：

showresult.ExecuteNonQuery();

这不会返回值，我不确定你为什么会有它

string actresult = ((string)shresult.ExecuteScalar());

除非您有一个 shresult 变量，否则此查询应该会出错。什么是 shresult 变量？

Answer 4

用于SqlParameter过滤结果和调用ExecuteScalar()或ExecuteReader()方法。

 string result = "SELECT ACTIVE FROM [dbo].[test] WHERE ID=@ID";
 SqlCommand showresult = new SqlCommand(result, conn);
 // If ID is int type
 showresult.Parameters.Add("@ID",SqlDbType.Int).Value=ID.Txt; 

 // If ID is Varchar then 
 //showresult.Parameters.Add("@ID",SqlDbType.VarChar,10).Value=ID.Txt; 

  conn.Open();
  string actresult = (string)showresult.ExecuteScalar(); 
  conn.Close();
  if(!string.IsNullOrEmpty(actresult))
       ResultLabel.Text = actresult;
  else
       ResultLabel.Text="Not found";

Answer 5

 conn.Open(); 
 string result = "SELECT ACTIVE FROM test WHERE ID = '" + ID.Text + "' ";
 SqlCommand showresult = new SqlCommand(result, conn);

 showresult.ExecuteNonQuery();
 int actresult = ((int)showresult.ExecuteScalar());
 ResultLabel.Text = actresult.Tostring();
 conn.Close();