Insert and Update Query

IF EXISTS(
SELECT 1
FROM MY_TABLE
WHERE ITEM='somevalue' AND ENTERDATE='12/31/1999')
--Update Statement
UPDATE MY_TABLE
SET ITEM='anothervalue'
WHERE ITEM='somevalue' AND ENTERDATE='12/31/1999'
ELSE
--Insert Statement
INSERT INTO MY_TABLE
(ITEM, ENTERDATE)
VALUES
('somevalue', '12/31/1999')