Cardinality Violation: 1241 Operand Should Contain 1 Column(S)

When am trying to execute this query

$followers = "(SELECT `user` FROM `follow` WHERE  `follower` LIKE '".$id."' )";

$onliners = "(SELECT * FROM `user_online` WHERE `user_id` IN $followers)";

$results = Yii::app()->db->createCommand("SELECT * FROM `ss_individual` where `id` IN $onliners")->queryAll();

I got this error:

CDbCommand failed to execute the SQL statement: SQLSTATE[21000]: Cardinality violation: 1241 Operand should contain 

1 column(s). The SQL statement executed was: SELECT * FROM `ss_individual` where `id` IN (SELECT * FROM `user_online` WHERE `user_id` IN (SELECT `user` FROM `follow` WHERE `follower` LIKE 'CMU1019' ))

How to solve this?

The statement … where id IN (SELECT * FROM user_online cannot work.

Must be something like … where id IN (SELECT user FROM user_online

Now only I saw that error and rectified. Thank you