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

4 files changed, 32 insertions, 0 deletions

diff --git a/lib/arel/engines/sql/extensions/array.rb b/lib/arel/engines/sql/extensions/array.rb
new file mode 100644
index 0000000000..1daa5abca7
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/array.rb
@@ -0,0 +1,9 @@
+class Array
+  def to_sql(formatter = nil)
+    "(" + collect { |e| e.to_sql(formatter) }.join(', ') + ")"
+  end
+
+  def inclusion_predicate_sql
+    "IN"
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/engines/sql/extensions/nil_class.rb b/lib/arel/engines/sql/extensions/nil_class.rb
new file mode 100644
index 0000000000..729c4cada7
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/nil_class.rb
@@ -0,0 +1,5 @@
+class NilClass
+  def equality_predicate_sql
+    'IS'
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/engines/sql/extensions/object.rb b/lib/arel/engines/sql/extensions/object.rb
new file mode 100644
index 0000000000..ef990eee2f
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/object.rb
@@ -0,0 +1,9 @@
+class Object
+  def to_sql(formatter)
+    formatter.scalar self
+  end
+
+  def equality_predicate_sql
+    '='
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/engines/sql/extensions/range.rb b/lib/arel/engines/sql/extensions/range.rb
new file mode 100644
index 0000000000..d7329efe34
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/range.rb
@@ -0,0 +1,9 @@
+class Range
+  def to_sql(formatter = nil)
+    formatter.range self.begin, self.end
+  end
+  
+  def inclusion_predicate_sql
+    "BETWEEN"
+  end
+end
\ No newline at end of file