How to get a distinct result ordered by a different column? SQL Postgresql -


i'm trying figure best way perform query in postgresql. have messages table , want grab last message user received each distinct user. need select row.

i think want group senders id "msgfromid", when complains haven't included select statement in group statement, want group 1 column, not of them. if try use distinct on 1 column forces me order 'distinct on' column first ("msgfromid") prevents me being able correct row need (ordered last message sent sender "msgsenttime").

my goal make efficient possible on server , database.

this have right now, not working. (this sub-query of query use join relevant information afterwards figure irrelevant)

select distinct on ("msgfromid") "msgfromid", "msgid", "msgtoid", "msgsenttime", "msgreadtime", "msgcontent", "msgreportstatus", "senderun", "recipientun"  "messages"   "msgtoid" = ? order "msgsenttime" desc, "msgfromid"

i thought maybe if pre-ordered them in sub-query work seems randomly pick 1 anyway, , can't efficient, if work, since i'm pulling every message out begin with, right?:

select distinct on ("msgfromid") "msgfromid", "msgid", "msgtoid", "msgsenttime", "msgreadtime", "msgcontent", "msgreportstatus", "senderun", "recipientun"               (      select * "messages"     "msgtoid" = ?     order "msgsenttime" desc   ) "mqo"

thanks help.

your order by keys in wrong order:

select distinct on ("msgfromid") m.* "messages" m  "msgtoid" = ? order "msgfromid", "msgsenttime" desc;

for distinct on, keys in parentheses need first keys in order by.

if want final result ordered in different way, need use subquery, different order by on outer query.


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