mysql 5.1.37 query index not being used

I have a query that is performing poorly. Server version: 5.1.37-1ubuntu5.1 (Ubuntu)

SELECT * FROM `influencers` WHERE (`influencers`.`twitter_id` = 86861293)  LIMIT 1

show create table influencers

influencers  CREATE TABLE `influencers` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`twitter_id` varch开发者_StackOverflowar(255) DEFAULT NULL,
`display_name` varchar(255) DEFAULT NULL,
`created_at` datetime DEFAULT NULL,
`updated_at` datetime DEFAULT NULL,
`screen_name` varchar(255) DEFAULT NULL,
 PRIMARY KEY (`id`),
 UNIQUE KEY `index_influencers_on_twitter_id` (`twitter_id`),
 KEY `influencers_screen_name` (`screen_name`)
 ) ENGINE=InnoDB AUTO_INCREMENT=504126 DEFAULT CHARSET=latin1  


explain SELECT * FROM `influencers` WHERE (`influencers`.`twitter_id` = 86861293)  LIMIT 1


id  select_type  table        type  possible_keys                    key     key_len  ref     rows    Extra        
--  -----------  -----------  ----  -------------------------------  ------  -------  ------  ------  -----------  
1   SIMPLE       influencers  ALL   index_influencers_on_twitter_id  (null)  (null)   (null)  553716  Using where  

The table has 547545 rows in it.

As you can see the explain has the possible key, but not showing it using the actual key.

Any ideas? Seems like this should work and im doing something dumb.

Since twitter_id is a VARCHAR, you should put the value in quotes in your WHERE clause to avoid any implicit type conversion that may prevent MySQL from using the optimal execution plan:

SELECT * 
FROM influencers
WHERE influencers.twitter_id = '86861293'
LIMIT 1