Does SQL Server Offer Anything Like MySQL's ON DUPLICATE KEY UPDATE

There's no DUPLICATE KEY UPDATE equivalent, but MERGE and WHEN MATCHED might work for you

Inserting, Updating, and Deleting Data by Using MERGE

I was surprised that none of the answers on this page contained an example of an actual query, so here you go:

A more complex example of inserting data and then handling duplicate

MERGEINTO MyBigDB.dbo.METER_DATA WITH (HOLDLOCK) AS targetUSING (SELECT    77748 AS rtu_id   ,'12B096876' AS meter_id   ,56112 AS meter_reading   ,'20150602 00:20:11' AS local_time) AS source(rtu_id, meter_id, meter_reading, time_local)ON (target.rtu_id = source.rtu_id  AND target.time_local = source.time_local)WHEN MATCHED  THEN UPDATE      SET meter_id = '12B096876'         ,meter_reading = 56112WHEN NOT MATCHED  THEN INSERT (rtu_id, meter_id, meter_reading, time_local)      VALUES (77748, '12B096876', 56112, '20150602 00:20:11');

You can try the other way around. It does the same thing more or less.

UPDATE tablename SET    field1 = 'Test1',        field2 = 'Test2' WHERE  id = 1 IF @@ROWCOUNT = 0   INSERT INTO tablename               (id,                field1,                field2)   VALUES      (1,                'Test1',                'Test2')