how to overwrite tuples in a table

Hi,

I have a table
pointattributes(pointid,attributeid,strvalue,numvalue)......where pointid
and attributeid are foreign keys refering to other tables. Now how can i
overwrite tuples in this table. To make it simpler,
pointid attributeid strvalue numvalue
----------------------------------------------------------------------
4 45 hello 3
7 50 hai 9

I want this table to retain the latest data.....
so if i say insert into pointattributes values(7,50,'Good Morning',10), it
should overwrite the previous tuple with this latest one. Is there a way to
do that.
One simple way is to check if there are any tuples with the given pointid
and attributeid, if a tuple exists delete the tuple with the pointid and
attribute(the combination is unique) and then insert the new tuple.
But is there any better way to do that.

Thanks in advance.

With Best Regards
Pradeep Kumar P J