Condition Compilation Question
- From: "Ethan Post" <post.ethan@xxxxxxxxx>
- To: oracle-l <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 15 May 2007 10:32:32 -0500
I am reading the section regarding conditional compilation here.
http://www.oracle.com/technology/pub/articles/10gdba/nanda_10gr2dba_part1.html#compile
What is the difference for the example below and using a standard "if then
else"? Why would below be better? Isn't it evaluated every time?
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Let's examine another variation of this new feature. In addition to the
definition of a conditional variable, you can also check a static constant
of a package in the conditional compilation. For example, suppose you want
to control the debugging output of a PL/SQL procedure based on a Boolean
packaged constant. First you create the package as
create or replace package debug_pkg
is
debug_flag constant boolean := FALSE;
end;
The debug_flag is the constant that determines the conditional logic in the
code. You can now embed the code inside the package as follows:
create or replace procedure myproc
as
begin
$if debug_pkg.debug_flag $then
dbms_output.put_line ('Debug=T');
$else
dbms_output.put_line ('Debug=F');
$end
end;
Note that the packaged constant is referenced directly without any $ sign.
In this case, there is no need to set any session- or system-level
conditional compilation parameters. While the function is compiled, you do
not need to pass any additional clause either. To see how this works,
execute:
SQL> exec myproc
Debug=F
Because the value of debug_pkg.debug_flag is FALSE now, the execution of the
procedure returned "F" as expected. Now, change the constant value:
create or replace package debug_pkg
is
debug_flag constant boolean := TRUE;
end;
Then, execute the procedure again:
SQL> exec myproc
Debug=T
The procedure picked up the value of the constant to show "T," as expected.
Note a very important difference here—you did not need to recompile the
procedure; the change to the constant was picked up automatically!
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