比如有这么个需求：
select F_command from bfb_db_finance . t_task where F_command like '%5025:%' and F_enabled = 1 limit 1 union all select F_command from bfb_db_finance . t_task where F_command like '%5026:%' and F_enabled = 1 order by F_task_id desc limit 1 ;
然后报错了：
ERROR 1054 (42S22): Unknown column 'F_task_id' in 'order clause'
解决方案：
select * from (select F_command from bfb_db_finance . t_task where F_command like '%5025:%' and F_command like '% 20161215 %' and F_enabled = 1 order by F_task_id desc limit 1 ) t5025 union all select * from (select F_command from bfb_db_finance . t_task where F_command like '%5026:%' and F_command like '% 20161215 %' and F_enabled = 1 order by F_task_id desc limit 1 ) t5026 union all select * from (select F_command from bfb_db_finance . t_task where F_command like '%5028:%' and F_command like '% 20161215 %' and F_enabled = 1 order by F_task_id desc limit 1 ) t5028 union all select * from (select F_command from bfb_db_finance . t_task where F_command like '%5027:%' and F_command like '% 20161215 %' and F_enabled = 1 order by F_task_id desc limit 1 ) t5027 union all select * from (select F_command from bfb_db_finance . t_task where F_command like '%5036:%' and F_command like '% 20161215 %' and F_enabled = 1 order by F_task_id desc limit 1 ) t5036;