1 files changed, 52 insertions, 4 deletions
diff --git a/activerecord/lib/arel/visitors/to_sql.rb b/activerecord/lib/arel/visitors/to_sql.rb
index 8e56fb55a2..f9fe4404eb 100644
--- a/activerecord/lib/arel/visitors/to_sql.rb
+++ b/activerecord/lib/arel/visitors/to_sql.rb
@@ -268,13 +268,11 @@ module Arel # :nodoc: all
         end
 
         def visit_Arel_Nodes_Union(o, collector)
-          collector << "( "
-          infix_value(o, collector, " UNION ") << " )"
+          infix_value_with_paren(o, collector, " UNION ")
         end
 
         def visit_Arel_Nodes_UnionAll(o, collector)
-          collector << "( "
-          infix_value(o, collector, " UNION ALL ") << " )"
+          infix_value_with_paren(o, collector, " UNION ALL ")
         end
 
         def visit_Arel_Nodes_Intersect(o, collector)
@@ -643,6 +641,26 @@ module Arel # :nodoc: all
           end
         end
 
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NULL"
+          else
+            collector = is_distinct_from(o, collector)
+            collector << " = 0"
+          end
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NOT NULL"
+          else
+            collector = is_distinct_from(o, collector)
+            collector << " = 1"
+          end
+        end
+
         def visit_Arel_Nodes_NotEqual(o, collector)
           right = o.right
 
@@ -845,6 +863,23 @@ module Arel # :nodoc: all
           visit o.right, collector
         end
 
+        def infix_value_with_paren(o, collector, value, suppress_parens = false)
+          collector << "( " unless suppress_parens
+          collector = if o.left.class == o.class
+            infix_value_with_paren(o.left, collector, value, true)
+          else
+            visit o.left, collector
+          end
+          collector << value
+          collector = if o.right.class == o.class
+            infix_value_with_paren(o.right, collector, value, true)
+          else
+            visit o.right, collector
+          end
+          collector << " )" unless suppress_parens
+          collector
+        end
+
         def aggregate(name, o, collector)
           collector << "#{name}("
           if o.distinct
@@ -858,6 +893,19 @@ module Arel # :nodoc: all
             collector
           end
         end
+
+        def is_distinct_from(o, collector)
+          collector << "CASE WHEN "
+          collector = visit o.left, collector
+          collector << " = "
+          collector = visit o.right, collector
+          collector << " OR ("
+          collector = visit o.left, collector
+          collector << " IS NULL AND "
+          collector = visit o.right, collector
+          collector << " IS NULL)"
+          collector << " THEN 0 ELSE 1 END"
+        end
     end
   end
 end