collapsing same table / column WHERE clauses to be OR [#4598 state:re…

…solved]

activerecord/lib/active_record/relation/query_methods.rb

@@ -176,10 +176,7 @@ def build_arel
 
       arel = build_joins(arel, @joins_values) unless @joins_values.empty?
 
-      (@where_values - ['']).uniq.each do |where|
-        where = Arel.sql(where) if String === where
-        arel = arel.where(Arel::Nodes::Grouping.new(where))
-      end
+      arel = collapse_wheres(arel, (@where_values - ['']).uniq)
 
       arel = arel.having(*@having_values.uniq.reject{|h| h.blank?}) unless @having_values.empty?
 
@@ -200,6 +197,30 @@ def build_arel
 
     private
 
+    def collapse_wheres(arel, wheres)
+      equalities = wheres.grep(Arel::Nodes::Equality)
+
+      groups = equalities.group_by do |equality|
+        left = equality.left
+        # table,             column
+        [left.relation.name, left.name]
+      end
+
+      groups.each do |_, eqls|
+        head = eqls.first
+        test = eqls.inject(head) do |memo, expr|
+          expr == head ? expr : memo.or(expr)
+        end
+        arel = arel.where(test)
+      end
+
+      (wheres - equalities).each do |where|
+        where = Arel.sql(where) if String === where
+        arel = arel.where(Arel::Nodes::Grouping.new(where))
+      end
+      arel
+    end
+
     def build_where(opts, other = [])
       case opts
       when String, Array