ops$tkyte@ORA920> create or replace context App_Ctx using My_pkg
  2  ACCESSED GLOBALLY
  3  /

Context created.

ops$tkyte@ORA920>
ops$tkyte@ORA920> create or replace package my_pkg
  2  as
  3          procedure set_ctx( p_name       in varchar2,
  4                                             p_value      in varchar2 );
  5
  6          procedure init;
  7  end;
  8  /

Package created.

ops$tkyte@ORA920>
ops$tkyte@ORA920> create or replace package body my_pkg
  2  as
  3          g_session_id number := 1234;
  4
  5          procedure init
  6          is
  7          begin
  8                  null;  -- elaboration code does it all
  9          end;
 10
 11          procedure set_ctx( p_name       in varchar2,
 12                                             p_value      in varchar2 )
 13          as
 14          begin
 15                  dbms_session.set_context
 16                  ( 'App_Ctx', p_name, p_value, NULL, g_session_id );
 17          end;
 18  begin
 19                  dbms_session.set_identifier( g_session_id );
 20  end;
 21  /

Package body created.

ops$tkyte@ORA920> pause

ops$tkyte@ORA920>
ops$tkyte@ORA920> exec my_pkg.set_ctx( 'Var1', 'Val1' );

PL/SQL procedure successfully completed.

ops$tkyte@ORA920> exec my_pkg.set_ctx( 'Var2', 'Val2' );

PL/SQL procedure successfully completed.

ops$tkyte@ORA920>
ops$tkyte@ORA920> select sys_context( 'app_ctx', 'var1' ) var1,
  2         sys_context( 'app_ctx', 'var2' ) var2
  3    from dual
  4  /

VAR1       VAR2
---------- ----------
Val1       Val2

ops$tkyte@ORA920>
ops$tkyte@ORA920> connect /
Connected.
ops$tkyte@ORA920>
ops$tkyte@ORA920> select sys_context( 'app_ctx', 'var1' ) var1,
  2         sys_context( 'app_ctx', 'var2' ) var2
  3    from dual
  4  /

VAR1       VAR2
---------- ----------


ops$tkyte@ORA920>
ops$tkyte@ORA920> exec my_pkg.init

PL/SQL procedure successfully completed.

ops$tkyte@ORA920>
ops$tkyte@ORA920> select sys_context( 'app_ctx', 'var1' ) var1,
  2         sys_context( 'app_ctx', 'var2' ) var2
  3    from dual
  4  /

VAR1       VAR2
---------- ----------
Val1       Val2

 

no example?

to use dbms_session.set_context, you have to be in the procedure, function or package that was bound to the context when you created it:

in the following ONLY P can set the context, no one else (that is what is magic about them)

ops$tkyte@ORA9IR2> create or replace context my_ctx using p
  2  /
 
Context created.
 
ops$tkyte@ORA9IR2>
ops$tkyte@ORA9IR2> create or replace procedure p
  2  as
  3  begin
  4          dbms_session.set_context( 'my_ctx', 'x', 5 );
  5  end;
  6  /
 
Procedure created.
 
ops$tkyte@ORA9IR2>
ops$tkyte@ORA9IR2> create or replace procedure p2
  2  as
  3  begin
  4          dbms_session.set_context( 'my_ctx', 'x', 5 );
  5  end;
  6  /
 
Procedure created.
 
ops$tkyte@ORA9IR2> exec dbms_session.set_context( 'my_ctx', 'x', 5 );
BEGIN dbms_session.set_context( 'my_ctx', 'x', 5 ); END;
 
*
ERROR at line 1:
ORA-01031: insufficient privileges
ORA-06512: at "SYS.DBMS_SESSION", line 78
ORA-06512: at line 1
 
 
ops$tkyte@ORA9IR2> exec p2
BEGIN p2; END;
 
*
ERROR at line 1:
ORA-01031: insufficient privileges
ORA-06512: at "SYS.DBMS_SESSION", line 78
ORA-06512: at "OPS$TKYTE.P2", line 4
ORA-06512: at line 1
 
 
ops$tkyte@ORA9IR2> exec p
 
PL/SQL procedure successfully completed.
 

I think it is poorly worded, what I believe they meant was:

ops$tkyte@ORA10G> select * from scott.emp where ename = sys_context( 'my_ctx', ename );
 
no rows selected


will work like a FUNCTION.....


but:

ops$tkyte@ORA10G> select * from scott.emp where ename = sys_context( 'my_ctx', 'X' );
 
no rows selected


will work like a bind - if the sys_context call returns a SINGLE value in the query, it'll be "bound", else it'll be treated much like a function would be. 

ops$tkyte%ORA11GR2> create or replace package my_pkg
  2  as
  3          g_global varchar2(20) := 'hello';
  4  end;
  5  /

Package created.

ops$tkyte%ORA11GR2> 
ops$tkyte%ORA11GR2> begin
  2          my_pkg.g_global := 'world';
  3          dbms_output.put_line( my_pkg.g_global );
  4  end;
  5  /
world

PL/SQL procedure successfully completed.

ops$tkyte%ORA11GR2> exec    dbms_session.reset_package;

PL/SQL procedure successfully completed.

ops$tkyte%ORA11GR2> set serveroutput on
ops$tkyte%ORA11GR2> begin
  2          dbms_output.put_line( my_pkg.g_global );
  3  end;
  4  /
hello

PL/SQL procedure successfully completed.