How to make effective index for search - mysql

Question

How to make the index on Table for speeding up searching.
I have two tables like these
(I created tables with doctorine from symfony2, but in fetching use plain mysql from python script.)
Now I want to exec this sql many times(changing x value)
select recordDate,closePrice from PriceDay where company_price=x ORDER BY recordDate DESC
So I wan to set the index like indexes={#ORM\Index(name="code_index",columns={"company_price","recordDate"})}) , but I am not sure it is the best solution or not. Pairs of company_price and recordDate are unique. Could you help some ideas??
* #ORM\Table(indexes={#ORM\Index(name="code_index",columns={"company_price","recordDate"})})
PriceDay table
class PriceDay
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #ORM\ManyToOne(targetEntity="Acme\UserBundle\Entity\Company")
* #ORM\JoinColumn(name="company_price", referencedColumnName="id")
*/
private $company;
/**
* #ORM\Column(type="float")
*/
private $closePrice = 0;
/**
*
* #ORM\Column(type="date")
*/
private $recordDate;
Company Table
class Company
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #ORM\Column(type="string",nullable=false)
*/
private $name;
/**
* #var boolean
* #ORM\Column(name="enabled",type="boolean")
*/
private $enabled = true;