Incorrect SQL generated for .last when ordering uses an SQL function

[vanyak]

I bumped into a problem with using COALESCE in sorting but it's relevant to any function like min or max.

When I have an order defined as COALESCE(t.field1, t.field2), all works great until .last is used. ActiveRecord was generating invalid SQL select whatever from t ORDER BY COALESCE(t.field1 DESC, t.field2 DESC) LIMIT 1.

[robin850]

Did you mean « order » here ?

[vanyak]

Sure, thanks.
Fixed.

[robin850]

/cc @rafaelfranca @tenderlove

[joxxoxo]

it's an old issue, please see #8225, #8741, though your solution looks nicer

[vanyak]

I tried to find if somebody has already fixed it before implementing myself. Apparently I did not search good enough.
Anyway I will be happy if any patch would be accepted.

[rafaelfranca]

@vanyak looks good. Could you apply the tests cases from the other two patches on you pull request and see if all work with your fix?

[joxxoxo]

actually i think they won't pass:
1.9.3p194 :001 > s='users.id asc, sum_fun(users.name, sum_other_fun(a, b, c), users.surname)'
=> "users.id asc, sum_fun(users.name, sum_other_fun(a, b, c), users.surname)"
1.9.3p194 :002 > s.split(/,(?=(?:[^)]|([^)]))$)/)
=> ["users.id asc, sum_fun(users.name, sum_other_fun(a, b, c), users.surname)"]

my solution from #8741:
..
1.9.3p194 :015 > s.scan(order_values_regexp).map(&:first)
=> ["users.id asc", " sum_fun(users.name, sum_other_fun(a, b, c), users.surname)"]

[vanyak]

@joxxoxo looks like you are right. There are actually some more cases when it won't work. Unfortunately Ruby does not support variable-length lookbehind assertions so the only way would be to use split like you did.
But I'll give it another try..

[vanyak]

Have to admit that trying further I came up with solution quite similar to the one @joxxoxo proposed.
Closing this one in favor of #8741

[carlosantoniodasilva]

@vanyak alright, thanks for reporting back.