在SAS中使用proc SQL返回最新值

Question

I'm looking to return the most recent result where the letter_source is "CCMA", based on the date the letter_type is "P29".

Basically I need to know the date of the last "CCMA" letter only for accounts which have had a "P29" letter. The CCMA letter can be any date as long as it's the most recent, but the P29 must be within a specific time period.

So far my code is:

proc sql;
   select distinct
      account_no        as account_no
     ,letter_date   as letter_date
     ,letter_type   as letter_type
     ,source        as letter_source
   from uulster.perm_aura_letters
   where letter_type="P29"
     and letter_date >= '01jul2015'd and letter_date <= '09jul2015'd
   order by letter_date, letter_type;
quit;

Please could you help?

Answer 1

proc sql;
select * from (select distinct
        account_no      as account_no
        ,letter_date    as letter_date
        ,letter_type    as letter_type
        ,source         as letter_source
        from uulster.perm_aura_letters
        where letter_type="P29"
        and letter_source contains "CCMA"
        and letter_date >= '01jul2015'd and letter_date <= '09jul2015'd)
having letter_date=max(letter_date)
order by letter_date, letter_type
;
quit;

Answer 2

I think you can do this using 2 perm letter tables. This isn't pretty but I'm not coming up with a more efficient way right now...

select distinct
    account_no      as account_no
    ,letter_date    as letter_date
    ,letter_type    as letter_type
    ,source         as letter_source
from uulster.perm_aura_letters p29
join uulster.perm_aura_letters ccma on p29.account_no = ccma.account_no
where p29.letter_type="P29"
and ccma.letter_type = "CCMA"
and p29.letter_date >= '01jul2015'd and p29.letter_date <= '09jul2015'd
and ccma.letterdate = (subselect max date for account and ccma)
order by p29.letter_date, p.29.letter_type

;