Add support for table aliasing

Example :
  users = Table(:users, :as => :accounts)
  users.to_sql
  => SELECT `accounts`.`id`, `accounts`.`name` FROM `users` AS `accounts`

2 files changed, 74 insertions, 2 deletions

diff --git a/spec/arel/engines/sql/unit/relations/join_spec.rb b/spec/arel/engines/sql/unit/relations/join_spec.rb
index 2820763a66..e2fc4bab3d 100644
--- a/spec/arel/engines/sql/unit/relations/join_spec.rb
+++ b/spec/arel/engines/sql/unit/relations/join_spec.rb
@@ -5,13 +5,20 @@ module Arel
     before do
       @relation1 = Table.new(:users)
       @relation2 = Table.new(:photos)
-      @predicate = @relation1[:id].eq(@relation2[:user_id])
+      @predicate1 = @relation1[:id].eq(@relation2[:user_id])
+
+      @relation3 = Table.new(:users, :as => :super_users)
+      @relation4 = Table.new(:photos, :as => :super_photos)
+
+      @predicate2 = @relation3[:id].eq(@relation2[:user_id])
+      @predicate3 = @relation3[:id].eq(@relation4[:user_id])
     end
 
     describe '#to_sql' do
+
       describe 'when joining with another relation' do
         it 'manufactures sql joining the two tables on the predicate' do
-          sql = InnerJoin.new(@relation1, @relation2, @predicate).to_sql
+          sql = InnerJoin.new(@relation1, @relation2, @predicate1).to_sql
 
           adapter_is :mysql do
             sql.should be_like(%Q{
@@ -29,6 +36,51 @@ module Arel
             })
           end
         end
+
+        describe 'when joining with another relation with an aliased table' do
+          it 'manufactures sql joining the two tables on the predicate respecting table aliasing' do
+            sql = InnerJoin.new(@relation3, @relation2, @predicate2).to_sql
+
+            adapter_is :mysql do
+              sql.should be_like(%Q{
+                SELECT `super_users`.`id`, `super_users`.`name`, `photos`.`id`, `photos`.`user_id`, `photos`.`camera_id`
+                FROM `users` AS `super_users`
+                  INNER JOIN `photos` ON `super_users`.`id` = `photos`.`user_id`
+              })
+            end
+
+            adapter_is_not :mysql do
+              sql.should be_like(%Q{
+                SELECT "super_users"."id", "super_users"."name", "photos"."id", "photos"."user_id", "photos"."camera_id"
+                FROM "users" AS "super_users"
+                  INNER JOIN "photos" ON "super_users"."id" = "photos"."user_id"
+              })
+            end
+          end
+        end
+
+        describe 'when joining with two relations with aliased tables' do
+          it 'manufactures sql joining the two tables on the predicate respecting table aliasing' do
+            sql = InnerJoin.new(@relation3, @relation4, @predicate3).to_sql
+
+            adapter_is :mysql do
+              sql.should be_like(%Q{
+                SELECT `super_users`.`id`, `super_users`.`name`, `super_photos`.`id`, `super_photos`.`user_id`, `super_photos`.`camera_id`
+                FROM `users` AS `super_users`
+                  INNER JOIN `photos` AS `super_photos` ON `super_users`.`id` = `super_photos`.`user_id`
+              })
+            end
+
+            adapter_is_not :mysql do
+              sql.should be_like(%Q{
+                SELECT "super_users"."id", "super_users"."name", "super_photos"."id", "super_photos"."user_id", "super_photos"."camera_id"
+                FROM "users" AS "super_users"
+                  INNER JOIN "photos" AS "super_photos" ON "super_users"."id" = "super_photos"."user_id"
+              })
+            end
+          end
+        end
+
       end
 
       describe 'when joining with a string' do
diff --git a/spec/arel/engines/sql/unit/relations/table_spec.rb b/spec/arel/engines/sql/unit/relations/table_spec.rb
index 92e4549028..977eb343e3 100644
--- a/spec/arel/engines/sql/unit/relations/table_spec.rb
+++ b/spec/arel/engines/sql/unit/relations/table_spec.rb
@@ -26,6 +26,26 @@ module Arel
       end
     end
 
+    describe '#as' do
+      it "manufactures a simple select query using aliases" do
+        sql = @relation.as(:super_users).to_sql
+
+        adapter_is :mysql do
+          sql.should be_like(%Q{
+            SELECT `super_users`.`id`, `super_users`.`name`
+            FROM `users` AS `super_users`
+          })
+        end
+
+        adapter_is_not :mysql do
+          sql.should be_like(%Q{
+            SELECT "super_users"."id", "super_users"."name"
+            FROM "users" AS "super_users"
+          })
+        end
+      end
+    end
+
     describe '#column_for' do
       it "returns the column corresponding to the attribute" do
         @relation.column_for(@relation[:id]).should == @relation.columns.detect { |c| c.name == 'id' }