From 4762adc5e671743030a2cadfa43e25c002e4295f Mon Sep 17 00:00:00 2001
From: Aidan Haran <aidanharan@yahoo.com>
Date: Tue, 19 Sep 2023 16:27:40 +0100
Subject: [PATCH 1/2] Fix tests in NullRelationTest

---
 .../sqlserver/core_ext/calculations.rb        | 33 +++++++++++++++----
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb b/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb
index da0e37f80..0853cd35d 100644
--- a/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb
+++ b/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb
@@ -8,18 +8,41 @@ module ConnectionAdapters
     module SQLServer
       module CoreExt
         module Calculations
-          # Same as original except we don't perform PostgreSQL hack that removes ordering.
           def calculate(operation, column_name)
-            return super unless klass.connection.adapter_name == "SQLServer"
+            if klass.connection.sqlserver?
+              _calculate(operation, column_name)
+            else
+              super
+            end
+          end
+
+          private
+
+          # Same as original `calculate` method except we don't perform PostgreSQL hack that removes ordering.
+          def _calculate(operation, column_name)
+            operation = operation.to_s.downcase
+
+            if @none
+              case operation
+              when "count", "sum"
+                result = group_values.any? ? Hash.new : 0
+                return @async ? Promise::Complete.new(result) : result
+              when "average", "minimum", "maximum"
+                result = group_values.any? ? Hash.new : nil
+                return @async ? Promise::Complete.new(result) : result
+              end
+            end
 
             if has_include?(column_name)
               relation = apply_join_dependency
 
-              if operation.to_s.downcase == "count"
+              if operation == "count"
                 unless distinct_value || distinct_select?(column_name || select_for_count)
                   relation.distinct!
-                  relation.select_values = [klass.primary_key || table[Arel.star]]
+                  relation.select_values = [ klass.primary_key || table[Arel.star] ]
                 end
+                # PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT
+                # relation.order_values = [] if group_values.empty?
               end
 
               relation.calculate(operation, column_name)
@@ -28,8 +51,6 @@ def calculate(operation, column_name)
             end
           end
 
-          private
-
           def build_count_subquery(relation, column_name, distinct)
             return super unless klass.connection.adapter_name == "SQLServer"
 

From 9e03b0391f1977bd7df307d004ae3c2fa96f9050 Mon Sep 17 00:00:00 2001
From: Aidan Haran <aidanharan@yahoo.com>
Date: Tue, 19 Sep 2023 16:37:14 +0100
Subject: [PATCH 2/2] Cleanup

---
 .../sqlserver/core_ext/calculations.rb               |  2 ++
 .../sqlserver/core_ext/finder_methods.rb             | 12 ++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb b/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb
index 0853cd35d..34355ef53 100644
--- a/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb
+++ b/lib/active_record/connection_adapters/sqlserver/core_ext/calculations.rb
@@ -42,7 +42,9 @@ def _calculate(operation, column_name)
                   relation.select_values = [ klass.primary_key || table[Arel.star] ]
                 end
                 # PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT
+                # Start of monkey-patch
                 # relation.order_values = [] if group_values.empty?
+                # End of monkey-patch
               end
 
               relation.calculate(operation, column_name)
diff --git a/lib/active_record/connection_adapters/sqlserver/core_ext/finder_methods.rb b/lib/active_record/connection_adapters/sqlserver/core_ext/finder_methods.rb
index 03932d492..fe9271508 100644
--- a/lib/active_record/connection_adapters/sqlserver/core_ext/finder_methods.rb
+++ b/lib/active_record/connection_adapters/sqlserver/core_ext/finder_methods.rb
@@ -10,18 +10,26 @@ module CoreExt
         module FinderMethods
           private
 
-          # Same as original except we order by values in distinct select if present.
           def construct_relation_for_exists(conditions)
-            return super unless klass.connection.adapter_name == "SQLServer"
+            if klass.connection.sqlserver?
+              _construct_relation_for_exists(conditions)
+            else
+              super
+            end
+          end
 
+          # Same as original except we order by values in distinct select if present.
+          def _construct_relation_for_exists(conditions)
             conditions = sanitize_forbidden_attributes(conditions)
 
             if distinct_value && offset_value
+              # Start of monkey-patch
               if select_values.present?
                 relation = order(*select_values).limit!(1)
               else
                 relation = except(:order).limit!(1)
               end
+              # End of monkey-patch
             else
               relation = except(:select, :distinct, :order)._select!(::ActiveRecord::FinderMethods::ONE_AS_ONE).limit!(1)
             end