adding a DISTINCT node

lib/arel/nodes/select_core.rb

@@ -2,15 +2,18 @@ module Arel
   module Nodes
     class SelectCore < Arel::Nodes::Node
       attr_accessor :top, :projections, :wheres, :groups
-      attr_accessor :having, :source
+      attr_accessor :having, :source, :set_quantifier
 
       def initialize
-        @source      = JoinSource.new nil
-        @top         = nil
-        @projections = []
-        @wheres      = []
-        @groups      = []
-        @having      = nil
+        @source         = JoinSource.new nil
+        @top            = nil
+
+        # http://savage.net.au/SQL/sql-92.bnf.html#set%20quantifier
+        @set_quantifier = nil
+        @projections    = []
+        @wheres         = []
+        @groups         = []
+        @having         = nil
       end
 
       def from

lib/arel/nodes/unary.rb

@@ -23,5 +23,11 @@ module Arel
     }.each do |name|
       const_set(name, Class.new(Unary))
     end
+
+    class Distinct < Unary
+      def initialize expr = nil
+        super
+      end
+    end
   end
 end

lib/arel/visitors/to_sql.rb

@@ -125,6 +125,7 @@ key on UpdateManager using UpdateManager#key=
         [
           "SELECT",
           (visit(o.top) if o.top),
+          (visit(o.set_quantifier) if o.set_quantifier),
           "#{o.projections.map { |x| visit x }.join ', '}",
           visit(o.source),
           ("WHERE #{o.wheres.map { |x| visit x }.join ' AND ' }" unless o.wheres.empty?),
@@ -137,6 +138,10 @@ key on UpdateManager using UpdateManager#key=
         visit o.expr
       end
 
+      def visit_Arel_Nodes_Distinct o
+        'DISTINCT'
+      end
+
       def visit_Arel_Nodes_With o
         "WITH #{o.children.map { |x| visit x }.join(', ')}"
       end

test/nodes/test_select_core.rb

@@ -1,22 +1,31 @@
 require 'helper'
 
-describe Arel::Nodes::SelectCore do
-  describe "#clone" do
-    it "clones froms, projections and wheres" do
-      core = Arel::Nodes::SelectCore.new
-      core.froms       = %w[a b c]
-      core.projections = %w[d e f]
-      core.wheres      = %w[g h i]
+module Arel
+  module Nodes
+    class TestSelectCore < MiniTest::Unit::TestCase
+      def test_clone
+        core = Arel::Nodes::SelectCore.new
+        core.froms       = %w[a b c]
+        core.projections = %w[d e f]
+        core.wheres      = %w[g h i]
 
-      dolly = core.clone
+        dolly = core.clone
 
-      dolly.froms.must_equal core.froms
-      dolly.projections.must_equal core.projections
-      dolly.wheres.must_equal core.wheres
+        dolly.froms.must_equal core.froms
+        dolly.projections.must_equal core.projections
+        dolly.wheres.must_equal core.wheres
 
-      dolly.froms.wont_be_same_as core.froms
-      dolly.projections.wont_be_same_as core.projections
-      dolly.wheres.wont_be_same_as core.wheres
+        dolly.froms.wont_be_same_as core.froms
+        dolly.projections.wont_be_same_as core.projections
+        dolly.wheres.wont_be_same_as core.wheres
+      end
+
+      def test_set_quantifier
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::Distinct.new
+        viz = Arel::Visitors::ToSql.new Table.engine
+        assert_match 'DISTINCT', viz.accept(core)
+      end
     end
   end
 end