SELECT username FROM users WHERE u_id = (SELECT TOP 1 u_id FROM images WHERE name = 'fYhWId')

或

SELECT username FROM users WHERE u_id IN (SELECT u_id FROM images WHERE name = 'fYhWId')

或

SELECT username,  s_id, images.u_id, name, filename, filesize 
FROM images 
INNER JOIN users on images.u_id = users.u_id
WHERE name = 'fYhWId'