SQL子查询是什么呢？

select 用户名 ,所处大区, 所处省区, sum(onduty_cnt) as onduty_cnt,sum(offduty_cnt) as offduty_cnt, sum(overtime) as overtime from (select 用户名 ,所处大区, 所处省区, onduty_time ,offduty_time, 打卡日期,overtime, case when to_char(onduty_time,'hh24:mi') > '09:00' then 1 else 0 end as onduty_cnt, case when to_char(offduty_time,'hh24:mi') < '17:20' then 1 else 0 end as offduty_cnt where 省区 = 参数 and 打卡日期 between '2009-01-01' and '2009-01-31' ) group by 用户名 ,所处大区, 所处省区

这是按人统计， 如果不要每个人的， 只要全部， 那就： select 所处大区, 所处省区, sum(onduty_cnt) as onduty_cnt,sum(offduty_cnt) as offduty_cnt, sum(overtime) as overtime from (select 用户名 ,所处大区, 所处省区, onduty_time ,offduty_time, 打卡日期,overtime, case when to_char(onduty_time,'hh24:mi') > '09:00' then 1 else 0 end as onduty_cnt, case when to_char(offduty_time,'hh24:mi') < '17:20' then 1 else 0 end as offduty_cnt where 省区 = 参数 and 打卡日期 between '2009-01-01' and '2009-01-31' ) group by 所处大区, 所处省区