Case when associated with group by

Today encountered a problem, the following are two ways to query, but the results of the query is not the same, the second query out the result is correct, if the first query Lendrequestid removed, the query results will be the same as the second, which is why?

1.SELECT Rr.lendrequestid,
(Case-rr.repaystate = ' Over_due_repaid ' then sum (rr.repayprincipal) end) as overdue repayment principal
From Dwloanrepayrecordfact RR
GROUP by Rr.lendrequestid
2.SELECT Rr.lendrequestid, sum (rr.repayprincipal)
From Dwloanrepayrecordfact RR
WHERE rr.repaystate = ' Over_due_repaid '
GROUP by Rr.lendrequestid

Case when associated with group by