New to PL/SQL, function question

Question

Hello guys,
I'm new to PL/SQL but have done C# and some Java.
Here is an example from a book I'm using:
declare
     v_pi_nr NUMBER:= 3.14;
     function f_getDiff_Nr(i_rad1_nr NUMBER, i_rad2_nr NUMBER)
     return NUMBER is
          v_area1_nr NUMBER;
          v_area2_nr NUMBER;
          v_out_nr NUMBER;
     function f_getArea_Nr(i_rad_nr NUMBER)
     return NUMBER
     is
     begin
          return v_pi_nr*(i_rad_nr**2); /inner
     end;
     begin
          v_area1_nr:= f_getArea_Nr(i_rad1_nr);
          v_area2_nr:= f_getArea_Nr(i_rad2_nr);
          v_out_nr  := v_area1_nr-v_area2_nr;
          return v_out_nr;             /outer
     end;
     begin
          DBMS_OUTPUT.put_line('Diff between 3 and 4:'||f_getDiff_Nr(4, 3));
          DBMS_OUTPUT.put_line('Diff between 4 and 5:'||f_getDiff_Nr(4, 3));
          DBMS_OUTPUT.put_line('Diff between 5 and 6:'||f_getDiff_Nr(4, 3));
     end;I'm wondering how it works, does outer function (f_getDiff_Nr) run first then passes the result to the inner function (f_getArea_Nr)?
Many thanks,
Mike
Edited by: mharper on 23-Oct-2011 14:35

Answer 1

Hi, Mike,
mharper wrote:
Hello guys,
I'm new to PL/SQL but have done C# and some Java.
Here is an example from a book I'm using:
declare
     v_pi_nr NUMBER:= 3.14;
     function f_getDiff_Nr(i_rad1_nr NUMBER, i_rad2_nr NUMBER)
     return NUMBER is
          v_area1_nr NUMBER;
          v_area2_nr NUMBER;
          v_out_nr NUMBER;
     function f_getArea_Nr(i_rad_nr NUMBER)
     return NUMBER
     is
     begin
          return v_pi_nr*(i_rad_nr**2); /inner
     end;
     begin
          v_area1_nr:= f_getArea_Nr(i_rad1_nr);
          v_area2_nr:= f_getArea_Nr(i_rad2_nr);
          v_out_nr  := v_area1_nr-v_area2_nr;
          return v_out_nr;             /outer
     end;
     begin
          DBMS_OUTPUT.put_line('Diff between 3 and 4:'||f_getDiff_Nr(4, 3));
          DBMS_OUTPUT.put_line('Diff between 4 and 5:'||f_getDiff_Nr(4, 3));
          DBMS_OUTPUT.put_line('Diff between 5 and 6:'||f_getDiff_Nr(4, 3));
     end;I'm wondering how it works, does outer function (f_getDiff_Nr) run first then passes the result to the inner function (f_getArea_Nr)?f_getDif_Nr gets called first. To do its job, f_getDiff_Nr calls f_getArea_Nr, which passes a NUMBER back to f_getDiff_Nr.
I think it's easier to understand indented and commented like this
declare     -- for anonymous block
    v_pi_nr NUMBER:= 3.14;
    function f_getDiff_Nr(i_rad1_nr NUMBER, i_rad2_nr NUMBER)
     return NUMBER is
          v_area1_nr NUMBER;
          v_area2_nr NUMBER;
          v_out_nr NUMBER;
          function f_getArea_Nr(i_rad_nr NUMBER)
          return NUMBER
          is
          begin     -- f_getArea-Nr body
               return v_pi_nr*(i_rad_nr**2); /inner
          end;     -- f_getArea-Nr body
     begin     -- f_getDiff_Nr body
          v_area1_nr:= f_getArea_Nr(i_rad1_nr);
          v_area2_nr:= f_getArea_Nr(i_rad2_nr);
          v_out_nr  := v_area1_nr-v_area2_nr;
          return v_out_nr;             /outer
     end;     -- f_getDiff_Nr body
begin     -- anonymous block body
     DBMS_OUTPUT.put_line('Diff between 3 and 4:'||f_getDiff_Nr(4, 3));
     DBMS_OUTPUT.put_line('Diff between 4 and 5:'||f_getDiff_Nr(4, 3));     -- Shouldn't the arguments be (5, 4)?
     DBMS_OUTPUT.put_line('Diff between 5 and 6:'||f_getDiff_Nr(4, 3));     -- Shouldn't the arguments be (6, 5)?
end;     f_getDiff_Nr is defined inside the anonymous block; that means it can only be called from within that anonymous block.
f_getArea_Nr is defined inside f_getDiff_Nr; that means it can only be called from within f_getArea_Nr. That's an unusual way to write functions. It's much more common to define functions inside a package, or to define them as stand-alone functions (that is, not within any other PL/SQL unit). Either way, they could be called from anywhere.
Edited by: Frank Kulash on Oct 23, 2011 7:52 PM