Fix merge_request_diffs migrations for postgresql

Former-commit-id: 4125de5e

db/migrate/20140122114406_migrate_mr_diffs.rb

 class MigrateMrDiffs < ActiveRecord::Migration
   def self.up
-    execute "INSERT INTO merge_request_diffs ( merge_request_id ) SELECT id FROM merge_requests"
-    execute "UPDATE merge_requests mr, merge_request_diffs md SET md.st_commits = mr.st_commits WHERE md.merge_request_id = mr.id"
-    execute "UPDATE merge_requests mr, merge_request_diffs md SET md.st_diffs = mr.st_diffs WHERE md.merge_request_id = mr.id"
+    execute "INSERT INTO merge_request_diffs ( merge_request_id, st_commits, st_diffs ) SELECT id, st_commits, st_diffs FROM merge_requests"
   end
   def self.down

db/migrate/20140122122549_remove_m_rdiff_fields.rb

@@ -7,7 +7,15 @@ class RemoveMRdiffFields < ActiveRecord::Migration
   def down
     add_column :merge_requests, :st_commits, :text, null: true, limit: 2147483647
     add_column :merge_requests, :st_diffs, :text, null: true, limit: 2147483647
-    execute "UPDATE merge_requests mr, merge_request_diffs md SET mr.st_commits = md.st_commits WHERE md.merge_request_id = mr.id"
-    execute "UPDATE merge_requests mr, merge_request_diffs md SET mr.st_diffs = md.st_diffs WHERE md.merge_request_id = mr.id"
+
+    if ActiveRecord::Base.connection.adapter_name == 'PostgreSQL'
+      execute "UPDATE merge_requests mr
+              SET (st_commits, st_diffs) = (md.st_commits, md.st_diffs)
+              FROM merge_request_diffs md
+              WHERE md.merge_request_id = mr.id"
+    else
+      execute "UPDATE merge_requests mr, merge_request_diffs md SET mr.st_commits = md.st_commits WHERE md.merge_request_id = mr.id"
+      execute "UPDATE merge_requests mr, merge_request_diffs md SET mr.st_diffs = md.st_diffs WHERE md.merge_request_id = mr.id"
+    end
   end
 end