Fix distinct alias when multiple databases used

Author: aidanharan

CHANGELOG.md

@@ -1,3 +1,9 @@
+## Unreleased
+
+#### Fixed
+
+- [#1262](https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/pull/1262) Fix distinct alias when multiple databases used.
+
 ## v7.1.9
 
 #### Fixed

lib/active_record/connection_adapters/sqlserver/schema_statements.rb

@@ -347,12 +347,16 @@ def add_timestamps(table_name, **options)
 
         def columns_for_distinct(columns, orders)
           order_columns = orders.reject(&:blank?).map { |s|
-                            s = s.to_sql unless s.is_a?(String)
+                            s = visitor.compile(s) unless s.is_a?(String)
                             s.gsub(/\s+(?:ASC|DESC)\b/i, "")
                              .gsub(/\s+NULLS\s+(?:FIRST|LAST)\b/i, "")
-                          }.reject(&:blank?).map.with_index { |column, i| "#{column} AS alias_#{i}" }
+                            }
+                            .reject(&:blank?)
+                            .reject { |s| columns.include?(s) }
 
-          (order_columns << super).join(", ")
+          order_columns_aliased = order_columns.map.with_index { |column, i| "#{column} AS alias_#{i}" }
+
+          (order_columns_aliased << super).join(", ")
         end
 
         def update_table_definition(table_name, base)

test/cases/adapter_test_sqlserver.rb

@@ -581,4 +581,13 @@ def test_doesnt_error_when_a_select_query_is_called_while_preventing_writes
       end
     end
   end
+
+  describe "distinct select query" do
+    it "generated SQL does not contain unnecessary alias projection" do
+      sqls = capture_sql do
+        Post.includes(:comments).joins(:comments).first
+      end
+      assert_no_match(/AS alias_0/, sqls.first)
+    end
+  end
 end