Merge pull request #139 from 8thlight/fix-migration-rollback

bring back transaction_id index when adding back transaction_id column

db/migrations/1525122581_associate_receipts_with_blocks.down.sql

@@ -3,6 +3,8 @@ BEGIN;
 ALTER TABLE receipts
   ADD COLUMN transaction_id INT;
 
+CREATE INDEX transaction_id_index ON receipts (transaction_id);
+
 UPDATE receipts
   SET transaction_id = (
     SELECT id FROM transactions WHERE transactions.hash = receipts.tx_hash
@@ -20,4 +22,4 @@ ON DELETE CASCADE;
 ALTER TABLE receipts
   DROP COLUMN block_id;
 
-COMMIT;
+COMMIT;