Не можете да ORDER BY
във вашия първи SELECT
и след това UNION
то.
Редактиране
Можете обаче
както в документацията на MySQL UNION
(SELECT a FROM t1 WHERE a=10 AND B=1 ORDER BY a LIMIT 10)
UNION
(SELECT a FROM t2 WHERE a=11 AND B=2 ORDER BY a LIMIT 10);
Което след това прави вашия SQL
(SELECT clicks FROM clicksTable WHERE clicks > 199 ORDER BY clicks ASC LIMIT 1)
UNION
(SELECT clicks FROM clicksTable ORDER BY clicks DESC LIMIT 1);
Редактиране 2
За връщане в array
SELECT (SELECT clicks
FROM clicksTable
WHERE clicks > 199
ORDER BY clicks ASC
LIMIT 1) AS NextClick,
(SELECT clicks
FROM clicksTable
ORDER BY clicks DESC
LIMIT 1) AS TopClick;