[absconder]

UPDATE db1_name.dbo.table1_name 
	SET db1_name.dbo.table1_name.soyad = (SELECT soyad FROM db2_name.dbo.table2_name WHERE db2_name.dbo.table2_name.id = 2) 
	WHERE db1_name.dbo.table1_name.id = 5

dbo yerine uygun kullanıcı adı da girilebilir.