MS SQL Invalid column name error

Question

This code returns the following error: "System.Data.SqlClient.SqlException (0x80131904): Invalid column name 'a51'"

a51 is the correct value inside of the record I'm looking for in the EstablishmentCode column of the Establishments table. Account ID is used to find all entries on the Establishments table with that account ID and populate a dataset with Establishment Code values. Account ID value comes from a session variable. Then I use each of these values in a loop where each iteration calls a datareader while loop. Hope I explained this clearly, but I would gladly clarify more if needed. Here's my code.

myConnection.Open();
SqlCommand getEst = new SqlCommand("SELECT EstablishmentCode FROM Establishments WHERE AccountID = " + ID, myConnection);
            da = new SqlDataAdapter(getEst);
            ds = new DataSet();
            da.Fill(ds);
            int maxrows = ds.Tables[0].Rows.Count;
            for (int x = 0; x < maxrows; x++)
            {
                getPhones = new SqlCommand("SELECT * FROM DispatcherPhones WHERE EstablishmentCode = " + ds.Tables[0].Rows[x].ItemArray.GetValue(0).ToString(), myConnection);
                myReader = getPhones.ExecuteReader();
                while (myReader.Read())
                {
                    Response.Write("<section id='phone" + myReader["Phone"].ToString() + "' style='padding:20px'>");
                    Response.Write("<section>Phone Number<br><div class='phone'>" + myReader["Phone"].ToString() + "</div></section>");
                    Response.Write("<section>Location Code<br><div class='name'>" + myReader["EstablishmentCode"].ToString() + "</div></section>");
                    Response.Write("<section>Active<br><div class='name'>" + myReader["Active"].ToString() + "</div></section>");
                    Response.Write("<section class='flex phoneButtonSection'>");
                    Response.Write("<button type=\"button\" onclick=\"showPhoneForm('" + myReader["ID"].ToString() + "');\">CHANGE</button>");
                    Response.Write("<button type=\"button\" onclick=\"deletePhones('" + myReader["ID"].ToString() + "');\">DELETE</button>");
                    Response.Write("</section>");
                    Response.Write("</section>");
                }
                myReader.Close();
            }

            myReader.Close();
            myConnection.Close();

Answer 1

String literals in SQL are denoted by single quotes ( ' s) which are missing for your value:

getPhones = new SqlCommand
    ("SELECT * " +
     "FROM DispatcherPhones 
     "WHERE EstablishmentCode = '" + 
     // Here -------------------^ 
     ds.Tables[0].Rows[x].ItemArray.GetValue(0).ToString() +
     "'" // And here
     , myConnection);

Mandatory comment: concatinating strings in order to create SQL statements may leave your code exposed to SQL injection attacks. You should consider using prepared statements instead.