//方式一
	$res = DB::table('merchant')
	    ->where('merchant_id', 1)
	    ->where('id', '>=', DB::raw('(SELECT floor(RAND() * (SELECT MAX(id) FROM `merchant`)))'))
	    ->first();
	//方式二（以下只支持mysql）
	$res = MerchantPos::where('merchant', 1)->inRandomOrder()->first();