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

2 files changed, 24 insertions, 0 deletions

diff --git a/lib/arel/engines/sql/relations/operations/alias.rb b/lib/arel/engines/sql/relations/operations/alias.rb
new file mode 100644
index 0000000000..32c9911a69
--- /dev/null
+++ b/lib/arel/engines/sql/relations/operations/alias.rb
@@ -0,0 +1,5 @@
+module Arel
+  class Alias < Compound
+    include Recursion::BaseCase
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/engines/sql/relations/operations/join.rb b/lib/arel/engines/sql/relations/operations/join.rb
new file mode 100644
index 0000000000..be21119bc9
--- /dev/null
+++ b/lib/arel/engines/sql/relations/operations/join.rb
@@ -0,0 +1,19 @@
+module Arel
+  class Join < Relation
+    def table_sql(formatter = Sql::TableReference.new(self))
+      relation1.externalize.table_sql(formatter)
+    end
+
+    def joins(environment, formatter = Sql::TableReference.new(environment))
+      @joins ||= begin
+        this_join = [
+          join_sql,
+          relation2.externalize.table_sql(formatter),
+          ("ON" unless predicates.blank?),
+          (ons + relation2.externalize.wheres).collect { |p| p.bind(environment).to_sql(Sql::WhereClause.new(environment)) }.join(' AND ')
+        ].compact.join(" ")
+        [relation1.joins(environment), this_join, relation2.joins(environment)].compact.join(" ")
+      end
+    end
+  end
+end
\ No newline at end of file