On duplicate key update

Question

I have had fairly good results with Oracles MySQL=>Oracle migration
tool in sqldeveloper... and now that DDL and data are converted I am starting
to wrestle with MySQL extensions and recoding them for oracle.... thus the
"on duplicate key update" interesting to say the least. Basically its a backward
upsert... in other words instead of the normal syntax
UPDATE my_table
SET mast_id = :b1
WHERE ...
IF SQL%NOTFOUND then
INSERT INTO my_table
VALUES ....
END IF;
Mysql will do something like
INSERT INTO my_table
VALUES ....
ON duplicate key update values( ... )
where the values are the ones from the insert....
has anyone have any suggestions or experience converting
this to oracle ...
also I have be seeing stuff like this
insert into week ( cal_day, cal_week ...)
     select cal_day
     @rownum:=if (@div=division,@rownum+1,1) as Position,
               @div:=division as dummy
     from
     ( select ..... from ....          
     ) stuff
     on duplicate key update
          Position=values(Position);
Is this @rownum:=if (@div=division,@rownum+1,1) as Position
some kind of CASE or DECODE beats me!
Any advice on converting MySQL procedures to Oracle PL/SQL
would be greatly appreciated

Answer 1

insert into week ( cal_day, cal_week ...)
select cal_day
@rownum:=if (@div=division,@rownum+1,1) as Position,
@div:=division as dummy
from
( select ..... from ....
) stuff
on duplicate key update
Position=values(Position);[pre]
the if then else part can be translate into oracle codes with the use of DECODE and/or CASE statement.
using a decode:
[pre]
  insert into week ([columns,...])
  select cal_day, decode(search , result [, search , result]... [, default] ),
    from [table]
using a case:
  insert into week ([columns,...])
  select cal_day, case when [condition] then [result]
                       when [condition] then [result]
                       else [result]
                  end
    from [table]