def self.order_by_number_of_comments_descending
select(‘titles.*, count(comments.id) AS comments_count’).
joins(:comments).
group(‘titles.id’).
order(‘comment_count DESC’)
end
results in a malformed SQL on Postgres,
SELECT COUNT(*) AS count_all, titles.id AS titles_id FROM “titles”
INNER JOIN “comments” ON “comments”.“title_id” = “titles”.“id” GROUP BY
titles.id ORDER BY comments_count DESC
I’ve contacted @steveklabnik and he’d re-open an issue reporting this
bug.https://github.com/rails/rails/issues/5588In the meantime, has
anybody got around this? The SQL is all correct until
you call group.
Thanks for helping
Your query is wrong…
You need group all columns you show that arent the result of an
aggregate
function…
So your group would be group(‘titles.*’)
Em 22/07/2013 18:22, “yaw” [email protected] escreveu:
def self.order_by_number_of_comments_descending
select(‘titles.id, titles.name, titles.whatever, count(comments.id)
AS
comments_count’).
joins(:comments).
group(‘titles.id, titles.name, titles.whatever’).
order(‘comment_count DESC’)
end
Assuming titles model is like (id, name, whatever)
The result query expected is:
SELECT COUNT(*) AS comments_count, titles.id AS titles_id, titles.name
as
titles_name, titles.whatever as titles_whatever FROM “titles”
INNER JOIN “comments” ON “comments”.“title_id” = “titles”.“id” GROUP
BY titles.id,
titles.name, titles.whatever http://titles.id ORDER BY comments_count
DESC
There are at least 2 problems with how you recommend the query to be
written:
Why would titles.* work in regular SQL but not in Rails’
selectmethod? What would be the case if I have 100 columns on the
titles table?
During grouping, the normal SQL requirement is to group on a
column
that is on both tables. As far as I know, grouping can’t be done on
two
tables when they don’t a common column. In your group call, only
titles.id would be useful. The rest won’t
Did you try running the resulting query? It should throw an exception
concerning the GROUP BY
On Tue, Jul 23, 2013 at 7:18 PM, Carlos Figueiredo < [email protected]> wrote:
Carlos Figueiredo
joins(:comments).
titles.name, titles.whatever http://titles.id ORDER BY comments_count
Can you write the right (no pun intended) query here? Thanks
group('titles.id').
I’ve contacted @steveklabnik and he’d re-open an issue reporting this
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On Jul 23, 2013, at 6:28 PM, Yaw Boakye elGran [email protected]
wrote:
During grouping, the normal SQL requirement is to group on a column that is
on both tables. As far as I know, grouping can’t be done on two tables when they
don’t a common column. In your group call, only titles.id would be useful. The
rest won’t
You seem to be confusing the grouping with the join condition. The join
requires 1 (usually, sometimes more) column common to both tables. The
grouping must include all columns not used in the aggregate function.
Sorry…
Are there more columns on titles entity? If yes… the problem is that
you
tried to show columns you weren’t grouping… and on postgresql it blows
an
exception… but if there is only one column on titles… (titles.id)
so, I
can’t figure out what’s the problem you mentioned…
What were your expected SQL to say that the result were malformed?
Atenciosamente,
Carlos Figueiredo
On Tue, Jul 23, 2013 at 4:11 PM, Carlos Figueiredo <
Now I figured out what is the error…
I dont know why… But rails changed the column name where you count
froum
comments_count to count_all… And you refer it on your order by
statement
using the alias you choose…
I hope somone more experienced on rails help you fix it, but for now…
U
could do 2 fix…
You can call the alias rails choose (count_all) on your order statement
(ugly way to solve)
Or you can call for count(*) without alias on your order statement (more
practiced by dba… Less ugly to solve)
Em 24/07/2013 07:40, “Yaw Boakye elGran” [email protected]
escreveu:
PG::Error: ERROR: column “comments_count” does not exist
LINE 1: …l, titles.created_at, titles.updated_at ORDER BY
comments_c…
^
: SELECT COUNT(*) AS count_all, titles.id, titles.title,
titles.submitter_name, titles.submitter_email, titles.created_at,
titles.updated_at AS
titles_id_titles_title_titles_submitter_name_titles_submitter_e FROM
“titles” INNER JOIN “comments” ON “comments”.“title_id” =
“titles”.“id” GROUP BY titles.id, titles.title, titles.submitter_name,
titles.submitter_email, titles.created_at, titles.updated_at ORDER BY
comments_count DESC
On Wed, Jul 24, 2013 at 10:38 AM, Yaw Boakye elGran [email protected]wrote:
