Is it possible to combine a select and insert statement into one statement? I would like to combine these two statements into a single database call.

Code:
SELECT tx.account_balance as last_balance
FROM transactions AS tx
INNER JOIN (
  SELECT MAX( txn_id ) AS last_tran
  FROM transactions
  WHERE user_id =63
) AS m ON tx.txn_id = m.last_tran

INSERT INTO transactions 
(user, value) 
VALUES
($user, last_balance+$amount )