Triggers and IO PLSQL

8/9/2019 Triggers and IO PLSQL

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Triggers

I/O and PL/SQL

Maria Luisa Yu

August 21, 2008


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INSTEAD OF Triggers

INSTEAD OF triggers control insert, update,

and delete operations on views, not tables.

They can be used to make nonupdateable

views updateable and to override the default

behavior of views that are updateable.


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INSTEAD OF Trigger Syntax

1 CREATE [OR REPLACE] TRIGGER trigger_name

2 INTEAD OF operation

3 ON view name

4 FOR EACH ROW

5 BEGIN

6 ... code goes here ...

7 END;


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The INSTEAD OF INSERT Trigger

1 CREATE [OR REPLACE] TRIGGER

trigger_name2 INTEAD OF INSERT

3 ON view name

4 FOR EACH ROW5 BEGIN


7 END;


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The INSTEAD OF UPDATE Trigger


trigger_name2 INTEAD OF UPDATE

3 ON view name



7 END;


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The INSTEAD OF DELETE Trigger


trigger_name2 INTEAD OF DELETE

3 ON view name



7 END;


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AFTER SUSPEND Triggers

a new type of trigger that fires whenever a

statement is suspended might occur as the result of a space issue such

as exceeding an allocated tablespace quota.

This functionality can be used to address the

problem and allow the stalled operation to

continue.


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AFTER SUSPEND Syntax

CREATE [OR REPLACE] TRIGGER trigger_name

AFTER SUSPEND

ON {DATABASE | SCHEMA}

BEGIN

... code ...

END;


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Maintaining Triggers

Oracle offers a number of DDL statements that

can help you manage your triggers. You can enable, disable, and drop triggers,

view information about triggers, and check the

status of triggers.


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Disabling Triggers

Disabling a trigger causes it not to fire when its

triggering event occurs. Dropping a trigger causes it to be removed

from the database altogether.

Syntax

ALTER TRIGGER trigger_name DISABLE;


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Enabling Triggers

A disabled trigger can also be reenabled asshown in the following example:

Syntax

ALTER TRIGGER emp_after_insert ENABLE;


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Dropping Triggers

Syntax

DROP TRIGGER emp_after_insert;


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Viewing Triggers

DBA_TRIGGERS

All triggers in the database ALL_TRIGGERS

All triggers accessible to the current user

USER_TRIGGERSAll triggers owned by the current user


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Checking the Validity of Triggers

Oddly enough, the trigger views in the data

dictionary do not display whether or not atrigger is in a valid state.

If a trigger is created with invalid PL/SQL, it is

saved in the database but marked as INVALID.

You can query the USER_OBJECTS orALL_OBJECTS views to determine this status.


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SQL> CREATE OR REPLACE TRIGGER

invalid_trigger 2 AFTER DDL ON SCHEMA

3BEGIN

4NULL

5END;

6/ Warning: Trigger created with compilation

errors.


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SQL> SELECT object_name,

2object_type,

3 status

4 FROM user_objects

5WHERE object_name = 'INVALID_TRIGGER';

OBJECT_NAME OBJECT TYPE STATUS------------- ----------- -------

INVALID_TRIGGER TRIGGER INVALID


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I/O and PL/SQL

most common mechanisms forI/O in PL/SQL, including the

following built-in packages:

DBMS_OUTPUT

For displaying information on the screen

UTL_FILE

For reading and writing operating system files

UTL_MAIL and UTL_SMTPFor sending email from within PL/SQL

UTL_HTTP

For retrieving data from a web page


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Enabling DBMS_OUTPUT

If DBMS_OUTPUT is disabled (default setting),

then calls to the PUT_LINE and PUT programsare ignored; the buffer remains empty.

To enable DBMS_OUTPUT, you will generally

execute a command in the host environment.

SET SERVEROUTPUT ON


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Specify that you want the text displayed by

DBMS_OUTPUT wrapped at the SQL*Plus linelength.

This version respects integrity of "words."

SET SERVEROUTPUT ON FORMAT WORD_WRAPPED


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DBMS_OUTPUT wrapped at the SQL*Plus linelength. The wrapping occurs regardless of

word separation. The wrapping occurs

regardless of word separation.

SET SERVEROUTPUT ON FORMAT WRAPPED


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Set the buffer size to the maximum allowed

prior to Oracle Database 10g Release 2:SET SERVEROUTPUT ON SIZE 1000000

Set the buffer size to "unlimited" (Oracle

Database 10g Release 2 only):

SET SERVEROUTPUT ON


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Write Lines to a Buffer

Call DBMS_OUTPUT.PUT_LINE or

DBMS_OUTPUT.PUT to put information intothe buffer.

PUT_LINE adds a newline marker after its text.

PUT places text in the buffer without a newline

marker.


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DBMS_OUTPUT to be truncated at theSQL*Plus line length; the rest of the text will

not be displayed.

SET SERVEROUTPUT ON FORMAT TRUNCATED

Turn off output in SQL*Plus:SET SERVEROUTPUT OFF


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Example

BEGIN

DBMS_OUTPUT.put_line ('Steven');DBMS_OUTPUT.put_line (100);DBMS_OUTPUT.put_line (SYSDATE);

END;

/


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Read the Contents of a Buffer

If you need to obtain the contents of the

DBMS_OUTPUT buffer, you can call theGET_LINE

The GET_LINE procedure retrieves one line of

information from the buffer (up to the maximum

supported by DBMS_OUTPUT), and returns astatus value of 0 if successful.


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Here's an example that uses this program to

extract the next line from the buffer into a localPL/SQL variable: and GET_LINES procedures.


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FUNCTION get_next_line RETURN VARCHAR2

IS

return_value VARCHAR2

(2

55);get_status INTEGER;

BEGIN

DBMS_OUTPUT.GET_LINE (return_value, get_status);

IF get_status = 0

THEN

RETURN return_value;ELSE

RETURN NULL;

END IF;

END;


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Reference

Oracle PL/SQL Programming By

Steven Feuerstein,Bill Pribyl ...............................................

Publisher: O'Reilly

Pub Date: August 2005

ISBN: 0-596-00977-1

Pages: 1198

Documents

Triggers and IO PLSQL