举例:select count(distinct A.questno) from (select questno,fastdfsurl,docfastdfsurl,pngfastdfsurl from dm_questlabel.fact_quest_label_old_jk where fastdfsurl like 'group%' and docfastdfsurl like 'group%' and pngfastdfsurl like 'group%' and questinnersource=1 and isanswer=0 and isoption=0)A;
1.查询到的结果作为一个虚拟表必须有一个别名,如A;
2.然后可以对虚拟表A中字段进行操作;