Fix `count(:all)` with eager loading and having an order other than the driving table

This is a regression caused by 6beb4de.

In PostgreSQL, ORDER BY expressions must appear in SELECT list when
using DISTINCT.

When using `count(:all)` with eager loading, Active Record enforces
DISTINCT to count the driving table records only. 6beb4de was caused the
regression because `count(:all)` with DISTINCT path no longer removes
ORDER BY.

We need to ignore ORDER BY when DISTINCT is enforced, otherwise not
always generated valid SQL for PostgreSQL.

Fixes #31783.

1 files changed, 8 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index cb0b06cfdc..decd60c87f 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -131,7 +131,14 @@ module ActiveRecord
     def calculate(operation, column_name)
       if has_include?(column_name)
         relation = apply_join_dependency
-        relation.distinct! if operation.to_s.downcase == "count"
+
+        if operation.to_s.downcase == "count" && !distinct_value
+          relation.distinct!
+          # PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT
+          if (column_name == :all || column_name.nil?) && select_values.empty?
+            relation.order_values = []
+          end
+        end
 
         relation.calculate(operation, column_name)
       else