Difference between place holders and formulas ?

Question

hi all , i want to know what can i do with place holders , i can not do with formulas ?
when do i need to use place holders ??
thanks in advance

Answer 1

For a formula, you are only returning one value.
So... if a user sent in a parameter of :p_class_number = 101 and I wanted to build a title for my report then I could create a formula named :CF_Report_Title and set it to a Character Datatype with a width of 20 for example.  I could then go into the formula and create the following:
function CF_Report_TitleFormula return Char is
begin
   return 'Class Number ' || :p_class_number;
end;
In the layout I would then create a Field named something like F_Report_Title and in the property pallete I would set the source to by formula :CF_Report_Title
For the second example, I could create three more formula's just like I did above to compute the number of people in that class, the average test scores for that class, and the number of people that were absent at any particular time for that class, but instead of having all of those formula's I would personally create three placeholder columns and name them something like:
:CP_class_count
:CP_avg_scores
:CP_absent_count
In the property palette I would probably leave all of these as NUMBER(10) because for this example I am returning numbers.  I would then create a formula named :CF_class_info and set the Datatype to NUMBER(1).  In the actual formula, I would create a function that looked something like this:
function CF_Class_InfoFormula return Number is
begin
  -- Compute the class count
  select count (*)
      into :CP_class_count
      from class_detail
    where class_number = :p_class_number;
        and ...;
  -- Compute the Average Score
  select average(class_score)
      into :CP_class_count
      from class_scores
    where class_number = :p_class_number;
        and ...;
  -- Compute the Abscenses
  select average(class_score)
      into :CP_class_count
      from class_abscence
    where class_number = :p_class_number;
        and ...;
  -- Finished with this formula
   return 1;
end;
At this point, I have run the formula one time, but was able to populate three placeholders.  I can then create fields in the layout and reference these placeholders instead of having to create three separate formulas.  It works either way, it is just whatever you prefer to do because they would both work.