What does $$ (double dollar) mean in Oracle SQL? - sql

Question

This Create package query executes in a SQLPlus util cli without error -
create or replace package PACKAGE2 as
$if $$install_ad_zd_sys $then
procedure LOG( X_MODULE varchar2, X_LEVEL varchar2, X_MESSAGE varchar2);
function LITERAL(X_VALUE varchar2) return varchar2;
else procedure LOG_VER;
$end
end;
/
Just want to know what does double dollar mean here?
Is it a sqlplus specific keyword?
I tried running this whole block as part of jdbc but it gives error 'Invalid column index'. So, I am suspecting the sign is specific to sqlplus, but not able to find the meaning of it.
This is how I am executing the above sql in java jdbc
plSqlstatement = connection.prepareCall(sqlBuffer.toString());
//sqlBuffer contains the whole create package block
//like sqlBuffer.append("CREATE OR REPLACE
//PACKAGE ....").append("/n").append(..next Line) and so on.

Answer 1

It's an inquiry directive:
An inquiry directive provides information about the compilation environment.
An inquiry directive typically appears in the boolean_static_expression of a selection directive, ...
... which is how you are using it, as it's within the $if conditional compilation directive.
You would need to assign a value, which you don't seem to be doing in either execution. But it will compile anyway, through SQL*Plus or JDBC (as in this db<>fiddle).
If you are getting an error from your JDBC call then you need to look at how you are running it - particularly if you are making get/set calls for arguments, as the error message suggests - since there are no arguments to set or retrieve.