UPDATE FROM portability

Updating some rows in tab1 with corresponding values from tab2, pgsql style:

UPDATE tab1         SET value=T2.VALUE    FROM tab2 T2 WHERE T2.restr=1       AND tab1.key=T2.key
<<<<<<

The same for MSSQL:

UPDATE tab1         SET value=T2.VALUE    FROM tab1 T1       JOIN tab2 T2 ON T1.key=T2.Key       <<<<<< WHERE
T2.restr=1


I'm looking for a portable query style, without using a subquery in the 
SET clause (which could make things quite slow)
Any hints?

Regards,
Andreas