sql - 如何通过使用 PLSQL 仅更改年份而不更改日期或月份来更新日期列？

Question

我有一个包含信用卡记录的数据库表。其中一个字段是日期字段。如果年份小于 2010，我想通过将日期的年份部分更改为 2011 来更新此字段。据我发现，PLSQL 具有时间和月份的功能，但与年份无关（据我所知）。

Answer 1

这显示了如何

with cc as(
select to_date('12-jan-1999') as cdate from dual union all
select to_date('12-jan-1921') as cdate from dual union all
select to_date('12-jan-1900') as cdate from dual union all
select to_date('12-jan-2000') as cdate from dual union all
select to_date('12-jan-2010') as cdate from dual
)
select  to_date( to_char(cdate,'DD-MON')  ||'-2011','DD-MON-YYYY')
from cc
where cdate < to_date('01-JAN-2010','DD-MON-YYYY')
/

Answer 2

1 年 = 12 个月，因此减去 12 个月：

select add_months(sysdate,-12) from dual

Answer 3

以下是如何使用 add_months 处理闰年的方法。

with cc as( 
select to_date('12-jan-1999','dd-mon-yyyy') as cdate from dual union all 
select to_date('12-jan-1921','dd-mon-yyyy') as cdate from dual union all 
select to_date('29-feb-1904','dd-mon-yyyy') as cdate from dual union all 
select to_date('12-jan-2000','dd-mon-yyyy') as cdate from dual union all 
select to_date('12-jan-2010','dd-mon-yyyy') as cdate from dual 
) 
select add_months(cdate,(2011 - extract( year from cdate)) * 12)  
from cc 
where cdate < to_date('01-JAN-2010','DD-MON-YYYY');