select count(*),(select IF(count(*)=0,1, count(*))from t_sys_user a where a.user_id=''),count(*)/(select IF (count(*)=0,1, count(*))from t_sys_user a where a.user_id='')from t_sys_user b where b.user_id='';
有多个数据库,只有一个数据库上查出的结果使【0,null,null】
其他的数据库的结果都是【0,1,0.0000】