fix constraint in migration script

migrations/version_0.sql

@@ -22,8 +22,8 @@ CREATE TABLE IF NOT EXISTS TRANSACTIONS (
     merchant_address_latitude DECIMAL(9, 6),
     merchant_address_longitude DECIMAL(9, 6),
     is_fraud BOOLEAN,
-    -- Add unique constraint on (transaction_num, transaction_datetime)
-    CONSTRAINT unique_transaction UNIQUE (transaction_number, transaction_datetime)
+    -- Add unique constraint on transaction_number
+    CONSTRAINT unique_transaction UNIQUE (transaction_number)
 );
 
 -- Add index on transaction_number