Re: Some insight on the proper SQL would be appreciated

[Andy Colson <andy@xxxxxxxxxxxxxxx>]

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

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