Check on whether a person is subscribed to another person
Test

SELECT F.USER_ID, 
       F.FOLLOWER_ID, 
       U.USERNAME, 
       U.NAME, 
       U.LAST_LOGIN, 
       F2.FOLLOWER_ID IS NOT NULL AS IS_FOLLOWER
FROM FOLLOWERS AS F
INNER JOIN USERS AS U ON (U.USER_ID = F.USER_ID)
LEFT JOIN FOLLOWERS AS F2 ON F.FOLLOWER_ID = F2.FOLLOWER_ID
                         AND F2.USER_ID = 89
WHERE F.USER_ID = '46'