Question

for (int i = 0; i < final_query.Length; i++)
{
   con.Open();

   SqlCommand cmd=new SqlCommand("SELECT * fROM TableFFF WHERE Data="+final_query[i]);

   SqlDataReader rdr = cmd.ExecuteReader();

   while (rdr.Read())
   {
      string PatientName = (string)rdr[" Data "];
   }
}

I got that error

ExecuteReader: Connection property has not been initialized.

on this line

SqlDataReader rdr = cmd.ExecuteReader();

How can i fix it?

Answer 1

You need to pass the Connection to the SqlCommand

SqlCommand cmd=new SqlCommand("SELECT * fROM TableFFF WHERE Data="+final_query[i], con); 

But there are other errors:

• The call to con.Open() should be outside of the For loop

• Use and reuse Parameters, not string concatenation

  con.Open();   
  SqlCommand cmd=new SqlCommand("SELECT * fROM TableFFF WHERE Data=@data", con);   
  cmd.Parameters.AddWithValue("@data", 0); // Supposing final_query[i] is an Int32
  for (int i = 0; i < final_query.Length; i++)   
  {   
      cmd.Parameters["@data"].Value = final_query[i];   
      SqlDataReader rdr = cmd.ExecuteReader();   
      while (rdr.Read())   
      {   
          string PatientName = (string)rdr[" Data "];   
      }   
  }
  

And it is still not clear what you are supposing to do with the PatientName after the first round