Database

USE thisDb;
SHOW TABLES;

string thisDb = listViewDatabases.SelectedItems[0].Text;
string Sql = "Use " + thisDb + ";"  + " Show Tables; ";

try
                {
                    // Obtain the Tables in the Database
                    MySqlCommand Comm = new MySqlCommand(Sql, Conn);
                    MySqlDataAdapter da = new MySqlDataAdapter(Comm);
                    DataSet ds = new DataSet();
                    da.Fill(ds);

                    int count = ds.Tables[0].Rows.Count;
                    string[] tables = new string[count];

                    for (int i = 0; i < count; i++)
                    {
                        tables[i] = ds.Tables[0].Rows[i][0].ToString();
                        listViewDbTables.Items.Add(tables[i].ToString());
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error" + ex.Message, "Error");
                }

GetSchemaTable()

//suppose reader (of type MySqlDataReader) has been already created properly using a query like "select * from mytable;"

DataTable dt = reader.GetSchemaTable();

//get information for each column of the table
foreach (DataRow dr in dt.Rows) {
    //retrieve each property of the column
    foreach (DataColumn dc in dt.Columns) {
        //just an example
        Console.WriteLine(dc.ColumnName + " = " + dr[dc].ToString());
    }
    Console.WriteLine();
}

Select This, null That
from SomeTable

Union
Select This, That
from SomeTable
 left join ThatTable on ...

select 101
union
select null
union
select  102
union
select null

using (OleDbConnection con=new OleDbConnection(connectionString)) {
	con.Open();
	using (OleDbCommand cmd=new OleDbCommand("SELECT * FROM ["+tableName+"]", con)) {
		// ref: http://www.pcreview.co.uk/forums/getschema-columns-results-t2877051.html
		DbDataReader rdr=cmd.ExecuteReader(CommandBehavior.SchemaOnly);
		DataTable schema=rdr.GetSchemaTable();
		foreach (DataColumn col in schema.Columns) log("colName="+col.ColumnName);
	}
}