DBA Tips Archive for Oracle


Debugging PL/SQL with
the DBMS_OUTPUT Package

by Jeff Hunter, Sr. Database Administrator

One of Oracle's most widely used standard package for developers and DBAs is DBMS_OUTPUT. This package comes in very handy when needing to debug a PL/SQL program. DBMS_OUTPUT allows you to display information to your session's output device as your PL/SQL program executes. DBMS_OUTPUT also comes in handy when generating reports from PL/SQL that need to be run in SQL*Plus. The DBMS_OUTPUT package became available with PL/SQL Version 2.

Module Name Description
DISABLE procedure Disables output from the package. The DBMS_OUTPUT buffer will not not be flushed to the screen.
ENABLE procedure Enables output from the package.
GET_LINE procedure Gets a single line from the buffer.
GET_LINES procedure Gets specified number of lines from the buffer and passes them into a PL/SQL table.
NEW_LINE procedure Inserts an end-of-line mark in the buffer.
PUT procedure Puts information into the buffer.
PUT_LINE procedure Puts information into the buffer and appends an end-of-line marker after that data.

The buffer size can be set to a size between 2,000 and 1,000,000 bytes with the ENABLE procedure. The buffer can store only three different types of data - VARCHAR2, NUMBER and DATE in their internal representation. The buffer will be contained in the SGA of the database instance.

The following is an example of an anonymous PL/SQL block that uses DBMS_OUTPUT to display the name of all distinct users in the table USER_NAMES and a count of how many time their name appears:

      FOR user_rec IN
      (select name, count(*) Count from user_names group by name)
          ('Name: ' || user_rec.name || 
           '   (' || user_rec.count || ')');
      END LOOP;
The above code generates the following output when executed in SQL*Plus:
    Name: Abe Smith   (999)
    Name: Amy Brown   (1)
    Name: Default User   (16579)
    Name: John Smith   (2922)
Make sure that serveroutput is set to ON in SQL*Plus before executing the above code segment. If this value is not set to ON, you will not be able to see the output from the DBMS_OUTPUT packge. In a SQL*Plus session type:
    set serveroutput on

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Last modified on
Thursday, 10-Jun-1999 00:00:00 EDT
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