sql - 使用Case Statement比较四列并将最早的日期添加到新列

Question

我试图有一列列出四列中最早的日期。我已经尝试过这个案例声明和一个应该列出 s.Open_date 的 jar ，而是将 1/1/2020 放在列中。这是数据

tin     S.Open_Date     LoanOpen    CCOpenDate    MortgageDate    EarliestDate
1        5/5/2015        11/19/2018    null        9/25/2017         1/1/2020

因此，在上面的示例中，它的 EarliestDate 列中应该有 5/5/2015。
我已经把整个查询放在下面。也就是说，除了 Case Statement 之外，查询中的所有内容都可以正常工作。有没有更好的方法来做到这一点？

select i.mem, min(s.open_date) as ShareOpenDate, min(l.loanopen) as LoanOpen, min(ecc.cc_opendate) as CCopenDate, min(m.MortgageDate) as MortgageDate,

Case
when (s.open_date > l.loanopen and s.open_date > ecc.cc_opendate AND s.open_date > m.MortgageDate) then s.open_date
when (l.loanopen > s.open_date and l.loanopen > ecc.cc_opendate AND l.loanopen > m.MortgageDate) then l.loanopen
when (ecc.cc_opendate > s.open_date and ecc.cc_opendate > l.loanopen AND ecc.cc_opendate > m.MortgageDate) then ecc.cc_opendate
when (m.MortgageDate > s.open_date and m.MortgageDate > l.loanopen AND m.MortgageDate > ecc.cc_opendate) then m.MortgageDate
else '1/1/2020' END as EarliestDate

from individual as i
inner join membershipparticipant as mp on i.individual_id=mp.individual_id and mp.participation_type=101
inner join share as s on mp.member_nbr=s.member_nbr

#Subquery to bring in loan information
left outer join (
select member_nbr, min(open_date) as loanopen
from loan as l
group by member_nbr
)l  on s.member_nbr=l.member_nbr

#Subquery to bring in CC Information
left outer join ( 
select savings_acct_nbr, min(open_date) as cc_opendate
from externalcreditcard
group by savings_acct_nbr
) ecc on s.member_nbr=ecc.savings_acct_nbr

Subquery to bring in mortgage information
left outer join (
select MC_PMT_MBR_NBR as MortgageMember, min(MC_Loan_Date) as MortgageDate
from EXTERNALMORTGAGEMC
group by MC_PMT_MBR_NBR
)m on s.member_nbr=m.MortgageMember

group by i.mem

Answer 1

最简单的方法是在 SELECT 中使用子查询，虽然可能有一个小的性能影响:

SELECT
...
, (SELECT MIN(x)
    FROM (VALUES
      (l.loanopen),
      (s.open_date),
      (ecc.cc_opendate),
      (m.MortgageDate),
      ('1/1/2020')
   ) AS v (x)) AS EarliestDate
FROM ...