Question

For Postgresql 8.x, I have an answers table containing (id, user_id, question_id, choice) where choice is a string value. I need a query that will return a set of records (all columns returned) for all unique choice values. What I’m looking for is a single representative record for each unique choice. I also want to have an aggregate votes column that is a count() of the number of records matching each unique choice accompanying each record. I want to force choice to lowercase for this comparison to be made (HeLLo and Hello should be considered equal). I can’t GROUP BY lower(choice) because I want all columns in the result-set. Grouping by all columns causes all records to return, including all duplicates.

1. Closest I’ve gotten

select lower(choice), count(choice) as votes from answers where question_id = 21 group by lower(choice) order by votes desc;

The issue with this is it will not return all columns.

                     lower                     | votes 
-----------------------------------------------+-------
 dancing in the moonlight                      |     8
 pumped up kicks                               |     7
 party rock anthem                             |     6
 sexy and i know it                            |     5
 moves like jagger                             |     4

2. Trying with all columns

select *, count(choice) as votes from answers where question_id = 21 group by lower(choice) order by votes desc;

Because I am not specifying every column from the SELECT in my GROUP BY, this throws an error telling me to do so.

3. Specifying all columns in the GROUP BY

select *, count(choice) as votes from answers where question_id = 21 group by lower(choice), id, user_id, question_id, choice order by votes desc;

This simply dumps the table with votes column as 1 for all records.

How can I get the vote count and unique representative records from 1., but with all columns from the table returned?

Answer 1

Here’s what I ended up with:

SELECT answers.*, cc.votes as votes FROM answers join (
    select max(id) as id, count(id) as votes 
    from answers
    group by trim(lower(choice))
) cc 
on answers.id = cc.id ORDER BY votes desc, lower(response) asc