SELECT with WHERE IN and subquery extremely slow - mysql

Question

I want to exectute the following query:
SELECT *
FROM `bm_tracking`
WHERE `oid` IN
(SELECT `oid`
FROM `bm_tracking`
GROUP BY `oid` HAVING COUNT(*) >1)
The subquery:
SELECT `oid`
FROM `bm_tracking`
GROUP BY `oid`
HAVING COUNT( * ) >1
executes in 0.0525 secs
The whole query "stucks" (still processing after 3 minutes...). Column oid is indexed.
Table bm_tracking contains around 64k rows.
What could be the reason for this "stuck"?
[Edit: Upon request]
CREATE TABLE `bm_tracking` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`oid` varchar(10) NOT NULL,
`trk_main` varchar(50) NOT NULL,
`tracking` varchar(50) NOT NULL,
`label` text NOT NULL,
`void` int(11) NOT NULL DEFAULT '0',
`created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
KEY `oid` (`oid`),
KEY `trk_main` (`trk_main`),
KEY `tracking` (`tracking`),
KEY `created` (`created`)
) ENGINE=MyISAM AUTO_INCREMENT=63331 DEFAULT CHARSET=latin1
[Execution Plan]

Answer 1

Generally exists EXISTS faster than IN so you can try this and see if it executes better for you
SELECT *
FROM `bm_tracking` bt
WHERE EXISTS
( SELECT 1
FROM `bm_tracking` bt1
WHERE bt.oid = bt1.oid
GROUP BY `oid`
HAVING COUNT(*) >1
)
EDIT:
if you notice from the EXPLAIN you posted... the IN() is considered as a DEPENDENT SUBQUERY which is a correlated subquery... meaning that for every row in the table all rows in the table are pulled and compared... so for example 1000 rows in the table would mean 1000 * 1000 = 1 million comparisons -- thats why its taking such a long time