oracle,db2取上年末，上月末，上年同期

---上年末

select substr(to_char(
add_years(to_date('20200602','YYYYMMDD'),-1),'YYYYMMDD'
),1,4)||'1231'
from sysibm.dual

---上月末

select to_char(last_day
(add_months(to_date('20200602','YYYYMMDD'),-1)
),'YYYYMMDD' )
from sysibm.dual

---上年同期

select to_char(
add_months(to_date('20200602','YYYYMMDD'),-12)
,'YYYYMMDD' )
from sysibm.dual

oracle用dual

---取'20210321'日期所有季度的第一天

to_char(trunc(to_date('20210321','yyyymmdd'),'Q'),'yyyymmdd')=20210101

---取'20210421'日期上季度的最后一天（季末日期）

to_char(trunc(to_date('20210421','yyyymmdd'),'Q')-1,'yyyymmdd')=20210331

2021-07-03