CREATE OR REPLACE PROCEDURE process_transaction AS
v_balance    NUMBER(10,2);  
v_transfer   NUMBER(10,2) := 10000.00;  
BEGIN

SELECT account_balance 
INTO v_balance 
FROM user_accounts  
WHERE account_id = 12345; 

v_balance := v_balance + TO_NUMBER('2000.00');  

UPDATE user_accounts 
SET account_balance = v_balance - v_transfer
WHERE account_id = 12345;
COMMIT;
END process_transaction;

CREATE PROCEDURE process_transaction()
BEGIN
    DECLARE v_balance DECIMAL(10,2);  
    DECLARE v_transfer DECIMAL(10,2) DEFAULT 10000.00;  
    
    -- Retrieve account balance (row-level lock applied)
    SELECT account_balance 
    INTO v_balance 
    FROM user_accounts 
    WHERE account_id = 12345
    FOR UPDATE;  

    SET v_balance = v_balance + 2000.00;  
    
    UPDATE user_accounts 
    SET account_balance = v_balance - v_transfer
    WHERE account_id = 12345;

    COMMIT;
END;