Summary of DBMS_OUTPUT Subprograms

Table 43-2 DBMS_OUTPUT Package Subprograms

ENABLE Procedure

This procedure enables calls to PUT, PUT_LINE, NEW_LINE, GET_LINE, and GET_LINES. Calls to these procedures are ignored if the DBMS_OUTPUT package is not enabled.

If there are multiple calls to ENABLE, then buffer_size is the largest of the values specified. The maximum size is 1,000,000, and the minimum is 2,000.

Syntax

DBMS_OUTPUT.ENABLE (
   buffer_size IN INTEGER DEFAULT 20000);

Parameters

Table 43-3 ENABLE Procedure Parameters

Pragmas

pragma restrict_references(enable,WNDS,RNDS);

Errors

Table 43-4 ENABLE Procedure Errors

DISABLE Procedure

This procedure disables calls to PUT, PUT_LINE, NEW_LINE, GET_LINE, and GET_LINES, and purges the buffer of any remaining information.

As with ENABLE, you do not need to call this procedure if you are using the SERVEROUTPUT option of Enterprise Manager or SQL*Plus.

Syntax

DBMS_OUTPUT.DISABLE;

Pragmas

pragma restrict_references(disable,WNDS,RNDS);

PUT and PUT_LINE Procedures

You can either place an entire line of information into the buffer by calling PUT_LINE, or you can build a line of information piece by piece by making multiple calls to PUT. Both of these procedures are overloaded to accept items of type VARCHAR2, NUMBER, or DATE to place in the buffer.

All items are converted to VARCHAR2 as they are retrieved. If you pass an item of type NUMBER or DATE, then when that item is retrieved, it is formatted with TO_CHAR using the default format. If you want to use a different format, then you should pass in the item as VARCHAR2 and format it explicitly.

When you call PUT_LINE, the item that you specify is automatically followed by an end-of-line marker. If you make calls to PUT to build a line, then you must add your own end-of-line marker by calling NEW_LINE. GET_LINE and GET_LINES do not return lines that have not been terminated with a newline character.

If your line exceeds the buffer limit, then you receive an error message.

SQL> SET SERVER OUTPUT ON
SQL> BEGIN
     2 DBMS_OUTPUT.PUT_LINE ('hello');
     3 DBMS_LOCK.SLEEP (10);
     4 END;

Syntax

DBMS_OUTPUT.PUT      (item IN NUMBER);
DBMS_OUTPUT.PUT      (item IN VARCHAR2);
DBMS_OUTPUT.PUT      (item IN DATE);
DBMS_OUTPUT.PUT_LINE (item IN NUMBER);
DBMS_OUTPUT.PUT_LINE (item IN VARCHAR2);
DBMS_OUTPUT.PUT_LINE (item IN DATE);
DBMS_OUTPUT.NEW_LINE;

Parameters

Table 43-5 PUT and PUT_LINE Procedure Parameters

Errors

Table 43-6 PUT and PUT_LINE Procedure Errors

NEW_LINE Procedure

This procedure puts an end-of-line marker. GET_LINE(S) returns "lines" as delimited by "newlines". Every call to PUT_LINE or NEW_LINE generates a line that is returned by GET_LINE(S).

Syntax

DBMS_OUTPUT.NEW_LINE;

Errors

Table 43-7 NEW_LINE Procedure Errors

GET_LINE and GET_LINES Procedures

You can choose to retrieve from the buffer a single line or an array of lines. Call the GET_LINE procedure to retrieve a single line of buffered information. To reduce the number of calls to the server, call the GET_LINES procedure to retrieve an array of lines from the buffer.

You can choose to automatically display this information if you are using Enterprise Manager or SQL*Plus by using the special SET SERVEROUTPUT ON command.

After calling GET_LINE or GET_LINES, any lines not retrieved before the next call to PUT, PUT_LINE, or NEW_LINE are discarded to avoid confusing them with the next message.

Syntax

DBMS_OUTPUT.GET_LINE (
   line    OUT VARCHAR2,
   status  OUT INTEGER);

Parameters

Table 43-8 GET_LINE Procedure Parameters

Syntax

DBMS_OUTPUT.GET_LINES (
   lines       OUT  CHARARR,
   numlines    IN OUT  INTEGER);
 

CHARARR is a table of VARCHAR2(255).

Parameters

Table 43-9 GET_LINES Procedure Parameters

Example 1: Debugging Stored Procedures and Triggers

The DBMS_OUTPUT package is commonly used to debug stored procedures and triggers. This package can also be used to enable you to retrieve information about an object and format this output, as shown in "Example 2: Retrieving Information About an Object".

This function queries the employee table and returns the total salary for a specified department. The function includes several calls to the PUT_LINE procedure:

CREATE FUNCTION dept_salary (dnum NUMBER) RETURN NUMBER IS
   CURSOR emp_cursor IS
      SELECT sal, comm FROM emp WHERE deptno = dnum;
   total_wages    NUMBER(11, 2) := 0;
   counter        NUMBER(10) := 1;
BEGIN

   FOR emp_record IN emp_cursor LOOP
      emp_record.comm := NVL(emp_record.comm, 0);
      total_wages := total_wages + emp_record.sal
         + emp_record.comm;
      DBMS_OUTPUT.PUT_LINE('Loop number = ' || counter || 
         '; Wages = '|| TO_CHAR(total_wages));    /* Debug line */
      counter := counter + 1; /* Increment debug counter */
   END LOOP;
   /* Debug line */
   DBMS_OUTPUT.PUT_LINE('Total wages = ' ||
     TO_CHAR(total_wages));  
   RETURN total_wages;

END dept_salary;

Assume the EMP table contains the following rows:

EMPNO          SAL     COMM     DEPT
-----        ------- -------- -------
1002           1500      500      20
1203           1000               30
1289           1000               10
1347           1000      250      20

Assume the user executes the following statements in the Enterprise Manager SQL Worksheet input pane:

SET SERVEROUTPUT ON
VARIABLE salary NUMBER;
EXECUTE :salary := dept_salary(20);

The user would then see the following information displayed in the output pane:

Loop number = 1; Wages = 2000
Loop number = 2; Wages = 3250
Total wages = 3250

PL/SQL procedure successfully executed.

Example 2: Retrieving Information About an Object

In this example, the user has used the EXPLAIN PLAN command to retrieve information about the execution plan for a statement and has stored it in PLAN_TABLE. The user has also assigned a statement ID to this statement. The example EXPLAIN_OUT procedure retrieves the information from this table and formats the output in a nested manner that more closely depicts the order of steps undergone in processing the SQL statement.

 /****************************************************************/
/* Create EXPLAIN_OUT procedure. User must pass STATEMENT_ID to */
/* to procedure, to uniquely identify statement.                */
/****************************************************************/
CREATE OR REPLACE PROCEDURE explain_out 
   (statement_id IN VARCHAR2) AS 

   -- Retrieve information from PLAN_TABLE into cursor EXPLAIN_ROWS.

   CURSOR explain_rows IS 
      SELECT level, id, position, operation, options,
         object_name 
      FROM plan_table 
      WHERE statement_id = explain_out.statement_id 
      CONNECT BY PRIOR id = parent_id 
         AND statement_id = explain_out.statement_id 
      START WITH id = 0
       ORDER BY id; 
 
BEGIN 

   -- Loop through information retrieved from PLAN_TABLE:

   FOR line IN explain_rows LOOP 

      -- At start of output, include heading with estimated cost.

      IF line.id = 0 THEN 
         DBMS_OUTPUT.PUT_LINE ('Plan for statement '
            || statement_id
            || ', estimated cost = ' || line.position); 
      END IF; 

      -- Output formatted information. LEVEL determines indention level.

      DBMS_OUTPUT.PUT_LINE (lpad(' ',2*(line.level-1)) ||
         line.operation || ' ' || line.options || ' ' || 
         line.object_name); 
   END LOOP; 

END;