Added "from" method, allowing to specify custom from clauses.

3 files changed, 16 insertions, 2 deletions

diff --git a/lib/arel/engines/memory/relations/operations.rb b/lib/arel/engines/memory/relations/operations.rb
index 8e01938360..a5082715a1 100644
--- a/lib/arel/engines/memory/relations/operations.rb
+++ b/lib/arel/engines/memory/relations/operations.rb
@@ -32,6 +32,12 @@ module Arel
     end
   end
 
+  class From < Compound
+    def eval
+      unoperated_rows[sources..-1]
+    end
+  end
+
   class Group < Compound
     def eval
       raise NotImplementedError
diff --git a/lib/arel/engines/sql/formatters.rb b/lib/arel/engines/sql/formatters.rb
index 626803a887..a13e11f24f 100644
--- a/lib/arel/engines/sql/formatters.rb
+++ b/lib/arel/engines/sql/formatters.rb
@@ -98,6 +98,10 @@ module Arel
             (table.name != name_for(table) ? " AS " + quote_table_name(name_for(table)) : '')
         end
       end
+
+      def attribute(attribute)
+        attribute
+      end
     end
 
     class Attribute < WhereCondition
diff --git a/lib/arel/engines/sql/relations/relation.rb b/lib/arel/engines/sql/relations/relation.rb
index deca9b19cb..448cf7951d 100644
--- a/lib/arel/engines/sql/relations/relation.rb
+++ b/lib/arel/engines/sql/relations/relation.rb
@@ -13,7 +13,7 @@ module Arel
 
         query = build_query \
           "SELECT     #{select_clauses.kind_of?(::Array) ? select_clauses.join("") : select_clauses.to_s}",
-          "FROM       #{table_sql(Sql::TableReference.new(self))}",
+          "FROM       #{from_clauses}",
           (joins(self)                                   unless joins(self).blank? ),
           ("WHERE     #{where_clauses.join("\n\tAND ")}" unless wheres.blank?      ),
           ("GROUP BY  #{group_clauses.join(', ')}"       unless groupings.blank?   )
@@ -27,7 +27,7 @@ module Arel
       else
         build_query \
           "SELECT     #{select_clauses.join(', ')}",
-          "FROM       #{table_sql(Sql::TableReference.new(self))}",
+          "FROM       #{from_clauses}",
           (joins(self)                                   unless joins(self).blank? ),
           ("WHERE     #{where_clauses.join("\n\tAND ")}" unless wheres.blank?      ),
           ("GROUP BY  #{group_clauses.join(', ')}"       unless groupings.blank?   ),
@@ -51,6 +51,10 @@ module Arel
       parts.compact.join(" ")
     end
 
+    def from_clauses
+      sources.blank? ? table_sql(Sql::TableReference.new(self)) : sources
+    end
+
     def select_clauses
       attributes.collect { |a| a.to_sql(Sql::SelectClause.new(self)) }
     end