moved sql related code to its own engine area

Conflicts:

	lib/arel/engine.rb
	lib/arel/extensions/object.rb
	lib/arel/predicates.rb
	lib/arel/primitives/attribute.rb
	lib/arel/primitives/expression.rb
	lib/arel/primitives/value.rb
	lib/arel/relations/operations/join.rb
	lib/arel/relations/relation.rb
	lib/arel/relations/utilities/externalization.rb
	lib/arel/relations/utilities/nil.rb
	lib/arel/relations/writes/delete.rb
	lib/arel/relations/writes/insert.rb
	lib/arel/relations/writes/update.rb
	spec/arel/unit/relations/skip_spec.rb
	spec/arel/unit/relations/take_spec.rb
	spec/spec_helper.rb

3 files changed, 33 insertions, 0 deletions

diff --git a/lib/arel/engines/sql/relations/utilities/externalization.rb b/lib/arel/engines/sql/relations/utilities/externalization.rb
new file mode 100644
index 0000000000..1ac6f2de8e
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/externalization.rb
@@ -0,0 +1,14 @@
+module Arel
+  class Externalization < Compound
+    include Recursion::BaseCase
+
+    def table_sql(formatter = Sql::TableReference.new(relation))
+      formatter.select relation.select_sql, self
+    end
+
+    # REMOVEME
+    def name
+      relation.name + '_external'
+    end
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/engines/sql/relations/utilities/nil.rb b/lib/arel/engines/sql/relations/utilities/nil.rb
new file mode 100644
index 0000000000..77534b25ad
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/nil.rb
@@ -0,0 +1,6 @@
+module Arel
+  class Nil < Relation
+    def table_sql(formatter = nil); '' end
+    def name; '' end
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/engines/sql/relations/utilities/recursion.rb b/lib/arel/engines/sql/relations/utilities/recursion.rb
new file mode 100644
index 0000000000..848b059507
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/recursion.rb
@@ -0,0 +1,13 @@
+module Arel
+  module Recursion
+    module BaseCase
+      def table
+        self
+      end
+
+      def table_sql(formatter = Sql::TableReference.new(self))
+        formatter.table self
+      end
+    end
+  end
+end
\ No newline at end of file