Dbms Output Put Line

7/31/2019 Dbms Output Put Line

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DBMS_OUTPUT.PUT_LINEDBMS_OUTPUT.PUT_LINE allows you to write information to a bufferthroughout the execution of a trigger/procedure. That information isavailable to be read by a trigger/procedure (using GET_LINE(S)), or

dumped to SQL*Plus upon completion of execution.

One of the most common misconceptions is that PUT_LINE writes dataimmediately to SQL*Plus. That is not true. PUT_LINE only puts it in thebuffer. You will not see it before the block has executed. I can prove thatwith this example (note: you must load the user_lock package for this):

scott@Robert> BEGIN2 DBMS_OUTPUT.PUT_LINE('Going to sleep for 10 seconds...');3 USER_LOCK.SLEEP(1000);4 DBMS_OUTPUT.PUT_LINE('Woke up after 10 seconds.');

5 END;6 /Going to sleep for 10 seconds...Woke up after 10 seconds.

You will have seen both messages come out after 10 seconds asopposed to one before and one after.

Despite the fact that it doesn't write messages throughout its progress,PUT_LINE can still make a useful debugging tool. I like the way that themessages can be kept but easily disabled by using

DBMS_OUTPUT.DISABLE. Any PUT_LINE messages are silently ignored ifyou have DISABLEd DBMS_OUTPUT (or failed to ENABLE).

To see the messages, you need to call DBMS_OUTPUT.ENABLE. The onlyparameter is buffer_size, which, if NULL, will default to 20000. The buffersize can be anywhere from 2000 to 1000000.

scott@Robert> BEGIN2 DBMS_OUTPUT.DISABLE;3 DBMS_OUTPUT.PUT_LINE('Disabled');4 DBMS_OUTPUT.ENABLE;

5 DBMS_OUTPUT.PUT_LINE('Enabled');6 END;7 /Enabled

PL/SQL procedure successfully completed.

Incidentally, SQL*Plus's SET SERVEROUTPUT ON will call


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DBMS_OUTPUT.ENABLE. You can even use SIZE with that command. SETSERVEROUTPUT also includes formatting options, such as FORMATWRAPPED, WORD_WRAPPED and TRUNCATE (along with a SET LINESIZE)to get the output the way you want it. [EDIT: Fixed Typo]

There are two common errors related to DBMS_OUTPUT.PUT_LINE. Thefirst one is trying to put more than 255 characters per line.

scott@Robert> DECLARE2 l_string VARCHAR2(300);3 BEGIN4 l_string := '1234567890';5 l_string := l_string || l_string || l_string || l_string || l_string;6 l_string := l_string || l_string || l_string || l_string || l_string || l_string;7 DBMS_OUTPUT.PUT_LINE(l_string);8 END;

9 /DECLARE*ERROR at line 1:ORA-20000: ORU-10028: line length overflow, limit of 255 chars per lineORA-06512: at "SYS.DBMS_OUTPUT", line 35ORA-06512: at "SYS.DBMS_OUTPUT", line 133ORA-06512: at line 7

The solution here is to use DBMS_OUTPUT.NEW_LINE to split it up intolines. 255 is a hard limit, if you really want to print a line with more than

that, you can write your own package that does the same thing asDBMS_OUTPUT. That is actually a very common thing to do. Tom Kyte'shas a handy one in Appendix A of "Expert One-on-One Oracle."

The second common error is overfilling your buffer.

scott@Robert> BEGIN2 DBMS_OUTPUT.ENABLE(2000);3 FOR i IN 1..1000 LOOP4 DBMS_OUTPUT.PUT_LINE('This is line ' || i);5 END LOOP;

6 END;7 /This is line 1

This is line 105BEGIN*ERROR at line 1:


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ORA-20000: ORU-10027: buffer overflow, limit of 2000 bytesORA-06512: at "SYS.DBMS_OUTPUT", line 35ORA-06512: at "SYS.DBMS_OUTPUT", line 198ORA-06512: at "SYS.DBMS_OUTPUT", line 139ORA-06512: at line 4

The solution here is increase the size of your buffer, using ENABLE. Themaximum size is 1000000 and that is a hard limit. Once again, you canwrite your own package as a workaround.

This example also illustrated that even if you have an exception, thecontents of the buffer until that point is still available.

The alternative to writing your own package is to write your messages toa table. Then you can query the table at any time to see your debugmessages. DBMS_PIPE is another option to consider.

I will close with two more interesting "gotchas" forDBMS_OUTPUT.PUT_LINE.

scott@Robert> BEGIN2 DBMS_OUTPUT.PUT_LINE(' What happened to my leading spaces?');3 END;4 /

What happened to my leading spaces?

This is an SQL*Plus Gotcha. Just be sure to use FORMAT WRAPPED, like

so:

scott@Robert> SET SERVEROUTPUT ON FORMAT WRAPPEDscott@Robert> BEGIN2 DBMS_OUTPUT.PUT_LINE(' There they are!');3 END;4 /

There they are!

Here is the second gotcha.

scott@Robert> DECLARE2 l_bool BOOLEAN;3 BEGIN4 l_bool := TRUE;5 DBMS_OUTPUT.PUT_LINE(l_bool);6 END;7 /DBMS_OUTPUT.PUT_LINE(l_bool);


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*ERROR at line 5:ORA-06550: line 5, column 1:PLS-00306: wrong number or types of arguments in call to 'PUT_LINE'ORA-06550: line 5, column 1:

PL/SQL: Statement ignored

DBMS_OUTPUT.PUT_LINE is not overloaded for Booleans. The solution isto either to write your own package (as mentioned above), or convertfrom Boolean type to something else for the PUT_LINE call.

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Dbms Output Put Line