Re: Some insight on the proper SQL would be appreciated

>> 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