SELECT query from within a stored procedure

Question

DB Version:10gR2
For auditing purpose, i just want to execute the query within the IF condition, and get the results for spooling. But i am getting PLS-00428 error. Can't i just execute a SELECT query and get its results displayed in SQLPLUS so that i can spool them?
SQL> create or replace procedure ship_dtl_aud
  2  is
  3  v_exists number;
  4 
  5  begin
  6  
  7  Select count(1) into v_exists
  8  From ship_dtl
  9  WHERE track_code = 10
10  AND mod_date_time < SYSDATE - 1/(24*60);
11 
12   if v_exists>0
13   then
14            select s.username,s.sid, s.serial#, s.terminal,p.spid
15   from v$session s, v$process p
16   where s.paddr = p.addr and s.sid in (select SESSION_ID from V$LOCKED_OBJECT);
17 
18          end if; 
19  end;
20  /
Warning: Procedure created with compilation errors.
SQL> show errors
Errors for PROCEDURE ship_dtl_aud:
LINE/COL ERROR
14/11    PLS-00428: an INTO clause is expected in this SELECT statement

Answer 1

Within PL/SQL code, the results of a query have to be returned from the SQL engine to the PL/SQL engine, hence why it is asking you to include an INTO within your query. Note that the PL/SQL engine is running on the database server so it has no interface to display output to. To output from within PL/SQL you would have to write the data out yourself to whatever output you want e.g. use DBMS_OUTPUT to put the data to the standard output buffer (which can then be read by SQL*Plus if serveroutput is set to "on") or written out to a file on the server, or written out to a table.
You are assuming that because you can execute SQL from SQL*Plus and spool the output, you can do the same within PL/SQL. This is not the case. When SQL*Plus issues a SQL statement, it goes to the SQL engine and the results of that cursor (as an SQL query is a cursor) are collected by SQL*Plus and it displays them itself. When PL/SQL issues a SQL statement, it goes to the SQL engine and the results of that cursor come back to PL/SQL. PL/SQL doesn't have a display mechanism, so the results have to be collected INTO something.
Hope that's clear.