SQL, PL/SQL Expression and PL/SQL function

Question

In a Post Calculation Computation field I wanted the following computation:
if B is X
then
field = A
else
field = B
end if;
or as a decode
Decode(B,X,A,B)
I could not get this to work so I wrote a database function that simulates the decode. So when I put:
My_decode(B,X,A,B)
in the field it did work.
Basically I am not sure what kind of code one is expected to put into SQL, PL/SQL Expression and PL/SQL function fields. Can someone give an example of each? Also the APEX help is sometimes incorrect.
For example if you click the "Post Calculation Computation" label it says:
The For example, if this item is named P1_X, you could use post calculation expressions such as UPPER(:P1_X), INITCAP(:P2_Y), MIN(:P1_X,:P2_Y-200), NVL(:P1_X,:P2_Y), or a function call such as return my_func(:P1_X); to set the final value of the item.
But if you put return my_func(:P1_X); in the field you get an error. It should be just my_func(:P1_X);
thanks Rene

Answer 1

DECODE is only available in SQL, so would have to be used in a SQL Expression.Yes, that's what APEX keeps telling me when I use in in a field that has "SQL or PL/SQL expression" above it. So what do you put in the field?