gistfile1.txt

CREATE TABLE `accounts` (
  `account_id` int(11) NOT NULL AUTO_INCREMENT,
  `type` varchar(30) NOT NULL,
  `balance` decimal(9,2) DEFAULT NULL,
  PRIMARY KEY (`account_id`)
)

CREATE TABLE `transactions` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `date` datetime NOT NULL,
  `amount` decimal(9,2) DEFAULT NULL,
  `description` varchar(200) DEFAULT NULL,
  `account_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `transacts_to_accounts_fk` (`account_id`),
  CONSTRAINT `transacts_to_accounts_fk` FOREIGN KEY (`account_id`) REFERENCES `accounts` (`account_id`)
)

when I insert a new credit or debit in the transactions table

INSERT INTO transactions
VALUES ( null, now(), 1000, 'tax rebate', 1)

then i want the account balance updated 

UPDATE accounts
SET balance = +1000
WHERE account_id = 1


START TRANSACTION;
SELECT @A:=SUM(salary) FROM table1 WHERE type=1;
UPDATE table2 SET summary=@A WHERE type=1;
COMMIT