select query for checkbox search filter

[Vladimir Pazdera]

Hello,

I have a table:

CREATE TABLE `currencies` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(11) unsigned NOT NULL,
`currency` int(11) NOT NULL,
PRIMARY KEY (`id`),
CONSTRAINT `fk_user` FOREIGN KEY (`user_id`) REFERENCES user (`user_id`)
)

ID | USER_ID | CURRENCY
---------------------------------------
1 | 38 | EUR
2 | 38 | USD
3 | 38 | NOK
4 | 42 | EUR
5 | 42 | NOK
6 | 50 | USD

I'm trying to do search filter based on checkboxes with names of currency.
It would search in the table for all checked checkboxes related to user_id in the filter. So when for example currencies (EUR, USD, NOK) are checked then it would return only results of those users who has all three currencies. So in this case it would return only user_id #38. I tried to execute query "SELECT user_id FROM currencies WHERE currency IN ('EUR','USD','NOK')" but it returns results also when the user has just (USD), or (USD and EUR). Is there a way how to do it or my database structure are not so well constructed? Any suggestion how to to do it or rebuild the database will be appreaceated. Thanks in advance.