Re: Some insight on the proper SQL would be appreciated
От | Andy Colson |
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Тема | Re: Some insight on the proper SQL would be appreciated |
Дата | |
Msg-id | 4C0E962C.8040605@squeakycode.net обсуждение исходный текст |
Ответ на | Some insight on the proper SQL would be appreciated (Aaron Burnett <aburnett@bzzagent.com>) |
Список | pgsql-general |
>> On 6/8/2010 11:29 AM, Aaron Burnett wrote: >>> >>> Greetings, >>> >>> I hope this is the proper list for this, but I am a loss on how to achieve >>> one particular set of results. >>> >>> I have a table which is a list of users who entered a contest. They can >>> enter as many times as they want, but only 5 will count. So some users have >>> one entry, some have as many as 15. >>> >>> How could I distill this down further to give me a list that shows each >>> entry per user up to five entries per user? In other words, I need a >>> separate line item for each entry from each user up to the maximum of 5 rows >>> per user. >>> >>> Table looks like this: >>> username | firstname | lastname | signedup >>> --------------------------------------+-----------+-------------+----------- >>> - >>> ffc4bd0a-ccff-4203-a03c-4bd6b8c23a03 | Jean | Mathews | 2010-03-13 >>> ffc4bd0a-ccff-4203-a03c-4bd6b8c23a03 | Jean | Mathews | 2010-05-07 >>> ffc4bd0a-ccff-4203-a03c-4bd6b8c23a03 | Jean | Mathews | 2010-06-06 >>> ff8720d4-f808-4ee6-90e6-649872fdfa55 | Janis | Bunch | 2010-03-12 >>> ff48d89b-6afe-4ba0-8539-9683bec62c89 | Sandy | Yashnyk | 2010-04-25 >>> ff48d2a4-0637-4e46-9461-3dd0dc0d4d83 | Kendra | Elliott | 2010-05-09 >>> ff3a2a14-2575-44d5-b40b-3780f4d2506a | Kay | Maher | 2010-04-20 >>> fef7625b-d1e1-4c1a-bc82-d35a4a6db16d | Carolyn | Woodul | 2010-04-05 >>> fef21bbb-07a0-4c84-8708-4dc41b8b770b | Laurie | Montijo | 2010-04-03 >>> feee6473-af4d-4e70-b20c-a74ba08c000f | Geneva | Anderson | 2010-04-03 >>> feb690fc-0afb-4e87-b0d1-bdb2c4603fd1 | Judith | Astroff | 2010-06-05 >>> fea0f9a6-e89f-4dbd-b3fd-83efed27221f | Jennifer | Lavigne | 2010-02-09 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-03-20 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-03-27 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-03 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-10 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-17 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-25 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-05-01 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-05-08 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-05-16 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-05-22 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-05-30 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-06-06 >>> fe825a6d-6820-4282-b8e9-2e3cb9f660e8 | Susan | Stowe | 2010-03-12 >>> fe825a6d-6820-4282-b8e9-2e3cb9f660e8 | Susan | Stowe | 2010-03-15 >>> >>> But in John Smith's case where he has more than 5 entries, I would like >>> query results to limit him to just 5 entries to look like this: >>> >>> username | firstname | lastname | signedup >>> --------------------------------------+-----------+-------------+----------- >>> - >>> ffc4bd0a-ccff-4203-a03c-4bd6b8c23a03 | Jean | Mathews | 2010-03-13 >>> ffc4bd0a-ccff-4203-a03c-4bd6b8c23a03 | Jean | Mathews | 2010-05-07 >>> ffc4bd0a-ccff-4203-a03c-4bd6b8c23a03 | Jean | Mathews | 2010-06-06 >>> ff8720d4-f808-4ee6-90e6-649872fdfa55 | Janis | Bunch | 2010-03-12 >>> ff48d89b-6afe-4ba0-8539-9683bec62c89 | Sandy | Yashnyk | 2010-04-25 >>> ff48d2a4-0637-4e46-9461-3dd0dc0d4d83 | Kendra | Elliott | 2010-05-09 >>> ff3a2a14-2575-44d5-b40b-3780f4d2506a | Kay | Maher | 2010-04-20 >>> fef7625b-d1e1-4c1a-bc82-d35a4a6db16d | Carolyn | Woodul | 2010-04-05 >>> fef21bbb-07a0-4c84-8708-4dc41b8b770b | Laurie | Montijo | 2010-04-03 >>> feee6473-af4d-4e70-b20c-a74ba08c000f | Geneva | Anderson | 2010-04-03 >>> feb690fc-0afb-4e87-b0d1-bdb2c4603fd1 | Judith | Astroff | 2010-06-05 >>> fea0f9a6-e89f-4dbd-b3fd-83efed27221f | Jennifer | Lavigne | 2010-02-09 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-03-20 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-03-27 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-03 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-10 >>> fea0334e-4ae1-4599-b24d-9a5d8ce4fd37 | John | Smith | 2010-04-17 >>> fe825a6d-6820-4282-b8e9-2e3cb9f660e8 | Susan | Stowe | 2010-03-12 >>> fe825a6d-6820-4282-b8e9-2e3cb9f660e8 | Susan | Stowe | 2010-03-15 >>> >>> The username is unique for each user. >>> >>> pg version 8.25 on RHEL >>> >>> Any help in this would be greatly appreciated. >>> >>> Thank you. >>> >>> >> >> Ok, here we go. Add this function: >> >> CREATE OR REPLACE FUNCTION fifth(uid text) >> RETURNS timestamp without time zone >> LANGUAGE plpgsql >> IMMUTABLE >> AS $function$ >> declare >> result timestamp; >> begin >> select signedup into result from users where usename = uid >> order by signedup limit 1 offset 4; >> if not found then >> result = '1900-01-01'; >> end if; >> return result; >> end; >> $function$; >> >> >> >> I guessed at fieldnames and table names, so you'll have to edit as needed. >> >> Then you can run this: >> >> select * from users where signedup<= fifth(usename) order by usename, >> signedup; >> >> -Andy > On 6/8/2010 2:08 PM, Aaron Burnett wrote: > > thanks very much Andy. Very elegant. > > I do need to presere the users that have<5 entries though, so I think I can > modify your function to do that as well. > > Thanks again. > > > On 6/8/10 2:50 PM, "Andy Colson"<andy@squeakycode.net> wrote: > yeah, they should show up. If a username has < 5 rows, the function returns date '1900-01-01' and the query comes out: select * from users where signedup <= '1900-01-01' order by usename, signedup; ... of course, I didnt test this too much, it just "should" do it :-) -Andy
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