Question

C# code:

command = new SqlCommand(null, connection);
command = createSQLQuery(command); // returns a valid SQL Query that returns results in SQL Management Studio 2012
//dataGridView1.DataSource = GetData(command);
connection.Open();
SqlDataReader reader = command.ExecuteReader();
connection.Close();
dataGridView1.DataSource = GetData(command);
debugMySQL();

public DataTable GetData(SqlCommand cmd) {
    //SqlConnection con = new SqlConnection(connString);
    //SqlCommand cmd = new SqlCommand(sqlcmdString, cn);

    SqlDataAdapter da = new SqlDataAdapter(cmd);
    connection.Open();
    DataTable dt = new DataTable();
    da.Fill(dt);
    connection.Close();
    return dt;
}

I am using C# with WinForm and developing with Visual Studio 2012.

Answer 1

Your question is rather vague, but I’ll try to answer as best as I could.

I think, normally, you need to define the type of command that you are going to pass into the SqlCommand, before executing that command.

command.Commandtype = CommandType.StoredProcedure;

(OR)

command.CommandText = CommandType.Text;

You can set the SQL query in string value after that.

command.CommandText = ""; // your SQL query, or the name of the stored procedure


Also, you don’t need to set the DataSource of the grid twice. You only need to set it after you got the result of you SQL query execution is returned.
However you receive the result is your choice. But, you seemed to executed the command twice, with both GetData() method and command.ExecuteReader() method. And also, you are setting the DataSource of your grid twice too.

I think even if you managed to set up the command object properly, because of your double executions, data might be lost somehow between them.

And, by the way, what data type is returned from the createSQLQuery() method. You said it returned a valid SQL Query, but is it returned a valid sql query value in string, or your custom command object to parse into the SqlCommand?

I’ll include the best operable procedure I know for reading from the SQL database and bind that data into the grid control.

// I suppose you get the connection object as 'con'
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandType = CommandType.Text;
cmd.CommandText = "...";   // You desired SQL query goes here, or if you want to execute a stored procedure, set the command type as 'StoredProcedure' and text as sp name.

SqlDataAdapter dap = new SqlDataAdapter();
dap.SelectCommand = cmd;
DataTable tbl = new DataTable();
dap.Fill(tbl);
<br>
if (tbl.Rows.Count > 0)
{
    grid.DataSource = tbl;
    grid.DataBind();
}

I recommend you to receive the result as DataTable rather than SqlDataReader. Cause DataTable is more flexible and versatile.