Description:
------------
Hi
I have 60 tables from cls1 to cls60 and another 60 tables from subcls1 to subcls60.
When I join cls1 with subcls1 tables(from cls1 to cls20 and subcls1 to subcls20) and union these 40 tables toghther. It's work.
In the same condition, when I try to join and union 120 tables(three times as previous case) together, it can't work.
At that moment, I use strlen() try to figure out the length of the query string, the len is 33817.
Doesn't is a bug or does there have any system paramater that I need to change?
I appreciated.

Reproduce code:
---------------
select StsID, count(*) from (  
SELECT *  FROM  (  SELECT cls.ID, cls.IIGrpID, cls.IIID , subcls.*  FROM cls1 AS cls  LEFT JOIN (  SELECT AIID, ID, StsID, CIGrpID, CIID, RIGrpID, RIID  FROM subcls1 as subcls  ORDER BY StsID  ) AS subcls ON cls.ID = subcls.AIID  GROUP BY cls.ID  ) whole  LEFT JOIN  ( SELECT count( * ) AS num FROM subcls1 as subcls  GROUP BY AIID  ) AS subsum  ON whole.ID = subsum.AIID
UNION ??
UNION
SELECT *  FROM  (  SELECT cls.ID, cls.IIGrpID, cls.IIID , subcls.*  FROM cls60 AS cls  LEFT JOIN (  SELECT AIID, ID, StsID, CIGrpID, CIID, RIGrpID, RIID  FROM subcls60 as subcls  ORDER BY StsID  ) AS subcls ON cls.ID = subcls.AIID  GROUP BY cls.ID  ) whole  LEFT JOIN  ( SELECT count( * ) AS num FROM subcls60 as subcls  GROUP BY AIID  ) AS subsum  ON whole.ID = subsum.AIID
) as whole  group by StsID


Expected result:
----------------
I can got each status total number from the result.

Actual result:
--------------
StsID count(*)
1     6800
2     2600
3     4600
4     6200
5     3800