Question

我有一个表格，格式如下：

ID,FLAG,PERIOD
4,"C",7/19/2017
4,"C",7/22/2017
4,"R",7/22/2017
4,"R",7/26/2017

数据：

with temp as (
        select 4 as ID, 'R' as Flag, to_date('07/26/2017', 'mm/dd/yyyy') as Period from dual union
        select 4 as ID, 'R' as Flag, to_date('07/22/2017', 'mm/dd/yyyy') as Period from dual union
        select 4 as ID, 'C' as Flag, to_date('07/22/2017', 'mm/dd/yyyy') as Period from dual union 
        select 4 as ID, 'C' as Flag, to_date('07/19/2017', 'mm/dd/yyyy') as Period from dual)

我希望得到一个表示ID的结果，以及此max(Period)标志为“C”的ID是否大于相应的max(Period)标志为“R”的地方。

我想要的结果是（因为C的最大（期间）是22/7/2017，R的最大（期间）是26/07/2017：

ID  IS_GREATER
4   NO

我考虑过使用ID和Flag以及max（Period）进行查询，然后再做一个case语句。由于我是新手，我想知道有更好的方法吗？

Answer 1

with temp
     as (select 4 as ID, 'R' as Flag, to_date('07/26/2017', 'mm/dd/yyyy') as Period from dual
         union
         select 4 as ID, 'R' as Flag, to_date('07/22/2017', 'mm/dd/yyyy') as Period from dual
         union
         select 4 as ID, 'C' as Flag, to_date('07/22/2017', 'mm/dd/yyyy') as Period from dual
         union
         select 4 as ID, 'C' as Flag, to_date('07/19/2017', 'mm/dd/yyyy') as Period from dual
         union
         select 5 as ID, 'R' as Flag, to_date('07/26/2016', 'mm/dd/yyyy') as Period from dual
         union
         select 5 as ID, 'R' as Flag, to_date('07/22/2016', 'mm/dd/yyyy') as Period from dual
         union
         select 5 as ID, 'C' as Flag, to_date('07/22/2017', 'mm/dd/yyyy') as Period from dual
         union
         select 5 as ID, 'C' as Flag, to_date('07/19/2017', 'mm/dd/yyyy') as Period from dual)
  select ID
       , case
           when max(case when FLAG = 'C' then Period else null end) > max(case when FLAG = 'R' then Period else null end) then
             'Y'
           else
             'N'
         end
           is_greater
    from temp
group by ID;

在PLSQL中过滤比较

1 个答案: