run.rb

bot.command(:top10, in: "ma-fakka", description: "!top10") do |event|
	db = DB.new
	res = db.top10
  this_res = res.each_with_index.map { |r| "#{r['displayName']} #{r['gameScore']}" }
  // Print result from MySQL result like this
  // 1. name    score
  // 2. name    score
  // 3. name    score
  event.respond this_res
end

top10.rb

def top10
    begin
      con = Mysql2::Client.new(host: ENV['HOST'], username: 'root', password: '', database: ENV['DB'])
      res = con.query("SELECT displayName,gameScore FROM #{TABLE_NAME} ORDER BY gameScore DESC LIMIT 10")
      return res.to_a
    rescue Mysql2::Error => e
     puts "Error code: #{e.errno}"
     puts "Error message: #{e.error}"
     puts "Error SQLSTATE: #{e.sqlstate}" if e.respond_to?("sqlstate")
   ensure
     # disconnect from server
     con.close if con
   end
  end