将具有INNER JOIN，GROUP BY，ORDER BY和MAX（）的SQL查询转换为LINQ

Question

I am currently trying to convert the following SQL query:

SELECT ref.pa_nbr, MAX(ins.ins_id)
FROM referral ref
INNER JOIN ins i ON ref.referral_nbr = i.referral_nbr
INNER JOIN pm p ON i.pm_nbr = p.pm_nbr AND p.pm_group = 2
WHERE ref.pat_nbr = @pat_nbr
GROUP BY ref.pat_nbr
ORDER BY ref.pat_nbr

into a LINQ expression. I have tried several times but have not received the correct results. The latest attempt can be seen in the following:

var medicaidNumber = 
    (from referral in context.REFERRALs
     join ins in context.INSs on referral.REFERRAL_NBR equals ins.REFERRAL_NBR
     join pm in context.PMs on ins.PM_NBR equals pm.PM_NBR
     where referral.P_NBR == patid && pm.PM_GROUP == 2
     orderby referral.PAT_NBR
     group referral by referral.PAT_NBR).FirstOrDefault();

Could someone take a look at what I am doing and see if there's another way to go about this? Any help will be appreciated.

Answer 1

You have to group into a variable that you can then do the max aggregation on.

from referral in context.REFERRALs
join ins in context.INSs on referral.REFERRAL_NBR equals ins.REFERRAL_NBR
join pm in context.PMs on ins.PM_NBR equals pm.PM_NBR
where referral.P_NBR == patid && pm.PM_GROUP == 2
orderby referral.PAT_NBR
group ins.INS_Id by referral.PAT_NBR into grp
select new { PAT_NBR = grp.Key, MaxINSId = grp.Max() };