Same variable declaration in package

Question

Hi
Please go through below lines of code where I have declared same variable 2 times, which got compiled successfully. But If I do the same in stand alone procedure it throws an error. In case of creation of package it says package created. Can anyone justify to this .....
SQL> create or replace package
2 may221
3 as
4 a number := 10 ;
5 a number := 20 ;
6 procedure p1(a number) ;
7 end ;
8 /
Package created.
SQL> create or replace package body may221
2 as
3 procedure p1(a number)
4 as
5 begin
6 dbms_output.put_line(a) ;
7 end ;
8 end ;
9 /
Package body created.
SQL> set serverout on
SQL> exec may221.p1(20);
20
PL/SQL procedure successfully completed.
SQL> begin
2 dbms_output.put_line(may221.a) ;
3 end ;
4 /
dbms_output.put_line(may221.a) ;
ERROR at line 2:
ORA-06550: line 2, column 32:
PLS-00371: at most one declaration for 'MAY221.A' is permitted in the declaration section
ORA-06550: line 2, column 4:
PL/SQL: Statement ignored
Thanks and Regards
JC

Answer 1

> I checked it's working fine.. no errors..
Oracle version?
There is an error as there are two definitions of variable a. This will generate a run-time error when that variable is used.
However, the result of procedure P1 is not an error.
It is all a matter of scope. Scope determines the resolution of a reference (like a variable name, object name, column name, table name, etc.)
The scope is first local - which means the local code block is checked for resolution. And the variable a is found. In o-o terms, when you refer to variable a it is first resolved as self.a - and only when that fails, the scope changes to the "encapsulating" unit which is the package.
The following code illustrates:
SQL> create or replace package FooPackage is
2 a number := 10;
3 a number := 11;
4
5 procedure Show( a number );
6 end;
7 /
Package created.
SQL> show errors
No errors.
SQL>
SQL>
SQL> create or replace package body FooPackage is
2 procedure Show( a number ) is
3 begin
4 DBMS_OUTPUT.put_line( a ); -- <= resolved as self.a
5 end;
6 end;
7 /
Package body created.
SQL> show errors
No errors.
SQL>
SQL>
SQL> exec FooPackage.Show( 12 )
12
PL/SQL procedure successfully completed.
SQL> exec DBMS_OUTPUT.put_line( FooPackage.a );
BEGIN DBMS_OUTPUT.put_line( FooPackage.a ); END;
ERROR at line 1:
ORA-06550: line 1, column 40:
PLS-00371: at most one declaration for 'FOOPACKAGE.A' is permitted
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored