OCL3 Oracle 10 g : SQL & PL/SQL Session #9

1Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

OCL3 Oracle 10g:SQL & PL/SQLSession #9

Matthew P. Johnson

CISDD, CUNY

June, 2005


Agenda Triggers Transactions Oracle’s bulk loader

Go over some labs Do some more labs


New topic: Triggers PL/SQL programs that run automatically (are

“triggered”) when a certain event occurs

E.g.: on insert to some table On system start-up On delete from table

Big benefit: need not be called explicitly However row in table x is deleted, the trigger

gets called


Trigger events Trigger code may be “triggered” by many kinds of

events: Oracle start-up/shut-down

Triggers may replace initialization scripts

Data updates: Delete: maybe delete related rows Inserts Updates: maybe make other rows consistent Delete: maybe prevent

DDL statements Log creation of all objects, e.g.


Triggers Constraints state what must remain true

DBMS decides when to check Triggers are instructions to perform at explicitly

specified times

Three aspects: An event (e.g., update to an attribute) A condition (e.g., a test of that update value) An action (the trigger’s effect) (deletion, update, insertion)

When the event occurs, DBMS checks the constraint, and if it is satisfied, performs the action


DML trigger options The trigger may be:

Statement-level (e.g., a DELETE WHERE statement) or Row-level (e.g., for each row deleted)

The trigger may run BEFORE AFTER or INSTEAD OF the statement (in Oracle, not in others)

It may be triggered by INSERTs UPDATEs DELETEs


Trigger formCREATE [OR REPLACE] TRIGGER trigger name{BEFORE | AFTER | INSTEAD OF} {INSERT | DELETE | UPDATE | UPDATE OF column list} ON table name[FOR EACH ROW][WHEN (...)][DECLARE ... ]BEGIN ... executable statements ...[EXCEPTION ... ]END [trigger name];

CREATE [OR REPLACE] TRIGGER trigger name{BEFORE | AFTER | INSTEAD OF} {INSERT | DELETE | UPDATE | UPDATE OF column list} ON table name[FOR EACH ROW][WHEN (...)][DECLARE ... ]BEGIN ... executable statements ...[EXCEPTION ... ]END [trigger name];


Trigger type examples First run copy_tables.sql

1. statement_vs_row.sql INSERT INTO to_table SELECT * FROM from_table;

2. before_vs_after.sql INSERT INTO to_table SELECT * FROM from_table;

3. one_trigger_per_type.sql INSERT INTO to_table VALUES (1);

UPDATE to_table SET col1 = 10;DELETE to_table;


DML Trigger e.g.

Q: Why is this (maybe) better than client-side validation?

CREATE OR REPLACE TRIGGER validate_employee_changes BEFORE INSERT OR UPDATE ON employee FOR EACH ROWBEGIN check_age (:NEW.date_of_birth); check_resume (:NEW.resume);END;

CREATE OR REPLACE TRIGGER validate_employee_changes BEFORE INSERT OR UPDATE ON employee FOR EACH ROWBEGIN check_age (:NEW.date_of_birth); check_resume (:NEW.resume);END;


Triggers with WHEN

NB: WHEN applies only to row-level triggers

CREATE OR REPLACE TRIGGER check_raise AFTER UPDATE OF salary, commission ON employee FOR EACH ROWWHEN ((OLD.salary != NEW.salary OR (OLD.salary IS NULL AND NEW.salary IS NULL)) OR (OLD.commission != NEW.commission OR (OLD.commission IS NULL AND NEW.commission IS NULL)))BEGIN ...END;

CREATE OR REPLACE TRIGGER check_raise AFTER UPDATE OF salary, commission ON employee FOR EACH ROWWHEN ((OLD.salary != NEW.salary OR (OLD.salary IS NULL AND NEW.salary IS NULL)) OR (OLD.commission != NEW.commission OR (OLD.commission IS NULL AND NEW.commission IS NULL)))BEGIN ...END;


Triggers with WHEN Parentheses are required Can only call built-in functions in when

Packages like DBMS_OUTPUT are not allowed

CREATE OR REPLACE TRIGGER valid_when_clauseBEFORE INSERT ON frameFOR EACH ROWWHEN ( TO_CHAR(SYSDATE,'HH24') BETWEEN 9 AND 17 ) ...

CREATE OR REPLACE TRIGGER valid_when_clauseBEFORE INSERT ON frameFOR EACH ROWWHEN ( TO_CHAR(SYSDATE,'HH24') BETWEEN 9 AND 17 ) ...


Simple trigger example R(id, data, last-modified)

data is a large string Last-modified is a newly added date field

Goal: whenever data is modified, update last-modified date

Could modify all scripts/programs that touch this table Bad idea

Better: user a trigger

CREATE TRIGGER UpdateDateTriggerAFTER UPDATE OF data ON R

REFERENCING

NEW ROW AS NewTupleFOR EACH ROWBEGIN

NewTuple.last-modified = sysdate;END;

CREATE TRIGGER UpdateDateTriggerAFTER UPDATE OF data ON R

REFERENCING

NEW ROW AS NewTupleFOR EACH ROWBEGIN

NewTuple.last-modified = sysdate;END;


Multiple DML actions DML actions may be ORed together

CREATE OR REPLACE TRIGGER three_for_the_price_of_oneBEFORE DELETE OR INSERT OR UPDATE ON account_transactionFOR EACH ROWBEGINIF INSERTING THEN :NEW.created_by := USER; :NEW.created_date := SYSDATE;ELSIF DELETING THEN audit_deletion(USER,SYSDATE);END;

CREATE OR REPLACE TRIGGER three_for_the_price_of_oneBEFORE DELETE OR INSERT OR UPDATE ON account_transactionFOR EACH ROWBEGINIF INSERTING THEN :NEW.created_by := USER; :NEW.created_date := SYSDATE;ELSIF DELETING THEN audit_deletion(USER,SYSDATE);END;

To find actual action, check: INSERTING DELETING UPDATING


More on UPDATING UPDATING may be called for partic. columns

CREATE OR REPLACE TRIGGER validate_updateBEFORE UPDATE ON account_transactionFOR EACH ROWBEGIN IF UPDATING ('ACCOUNT_NO') THEN errpkg.raise('Account number cannot be updated'); END IF;END;

CREATE OR REPLACE TRIGGER validate_updateBEFORE UPDATE ON account_transactionFOR EACH ROWBEGIN IF UPDATING ('ACCOUNT_NO') THEN errpkg.raise('Account number cannot be updated'); END IF;END;


Extended auditing example Tables: grades, grades_audit Run: grades_tables.sql, grades_audit.sql Cases: hacker changes grades, deletes

others UPDATE gradesSET grade = 'A+'WHERE student_id = 1AND class_id = 101;

UPDATE gradesSET grade = 'A+'WHERE student_id = 1AND class_id = 101;

DELETE gradesWHERE student_id = 2AND class_id = 101;

DELETE gradesWHERE student_id = 2AND class_id = 101;


Extended auditing example Run: grades_tables.sql, grades_audit2.sql Cases: hacker changes student or class ids

UPDATE grades SET student_id = 3WHERE student_id = 1 AND class_id = 101;


UPDATE grades SET student_id = 2 WHERE student_id = 3 AND class_id = 101;



UPDATE grades SET student_id = 2 WHERE student_id = 3 AND class_id = 101;


DDL Triggers Respond to DDL events

Creating/dropping tables, indices, etc. ALTER TABLE etc.

General form:CREATE [OR REPLACE] TRIGGER trigger name{BEFORE | AFTER| {DDL event} ON

{DATABASE | SCHEMA}DECLARE Variable declarationsBEGIN... some code...END;

CREATE [OR REPLACE] TRIGGER trigger name{BEFORE | AFTER| {DDL event} ON

{DATABASE | SCHEMA}DECLARE Variable declarationsBEGIN... some code...END;


DDL trigger e.g. Town crier examples triggered by creates:

uninformed_town_crier.sql

informed_town_crier.sql


Available DDL events CREATE, ALTER, DROP, GRANT, RENAME,

REVOKE, TRUNCATE DDL: any DDL event

Q: Does this work??

CREATE OR REPLACE TRIGGER no_create AFTER CREATE ON SCHEMABEGIN RAISE_APPLICATION_ERROR (-20000,

'ERROR : Objects cannot be created in the production database.');

END;

CREATE OR REPLACE TRIGGER no_create AFTER CREATE ON SCHEMABEGIN RAISE_APPLICATION_ERROR (-20000,

'ERROR : Objects cannot be created in the production database.');

END;


DB Event triggers Form similar to DDL triggers:

Triggering events: STARTUP, SHUTDOWN, SERVERERROR, LOGON, LOGOFF

CREATE [OR REPLACE] TRIGGER trigger name{BEFORE | AFTER} {database event} ON {DATABASE | SCHEMA}DECLARE Variable declarationsBEGIN... some code...END;

CREATE [OR REPLACE] TRIGGER trigger name{BEFORE | AFTER} {database event} ON {DATABASE | SCHEMA}DECLARE Variable declarationsBEGIN... some code...END;


DB event restrictions Have BEFORE and AFTER as above, but they

don’t always apply:

No BEFORE STARTUP/LOGON/SERVERERROR

No AFTER SHUTDOWN/LOGOFF


DB Trigger e.g. Gather stats before shutdown:

Log error messages

CREATE OR REPLACE TRIGGER on_shutdownBEFORE SHUTDOWN ON DATABASEBEGIN gather_system_stats;END;

CREATE OR REPLACE TRIGGER on_shutdownBEFORE SHUTDOWN ON DATABASEBEGIN gather_system_stats;END;


Trigger maintenance Enabling & disabling:

ALTER TRIGGER emp_after_insert DISABLE; ALTER TRIGGER emp_after_insert ENABLE;

Deleting: DROP TRIGGER emp_after_insert;

Viewing: select trigger_name from user_triggers; select text from user_source where name='TOWN_CRIER';

Check validity: select object_name, status from user_objects where

object_type='TRIGGER';


Triggers – important points Can replace old row (result of event) with new row Action may be performed before or after event Can refer to old row and new row WHEN clauses tests whether to continue Action may be performed either

For each row involved in event Once per event

Oracle does triggers as PL/SQL programs A trigger runs in the same transaction as the event

triggering it


Elements of Triggers Timing of action execution: before, after or instead

of triggering event The action can refer to both the old and new state of

the database Update events may specify a particular column or

set of columns A condition is specified with an optional WHEN

clause The action can be performed either for

once for every tuple or once for all the tuples that are changed by the database

operation


Intermission Go over previous labs

Begin lab…

Break


New-old topic: Transactions So far, have simply issued commands

Ignored xacts

Recall, though: an xact is an operation/set of ops executed atomically In one instant

ACID test: Xacts are atomic Each xact (not each statement) must leave the DB

consistent


Default xact behavior An xact begins upon login By default, xact lasts until logoff

Except for DDL statements They automatically commit

Examples with two views of emp…


Direct xact instructions At any point, may explicitly COMMIT:

SQL> COMMIT; Saves all statements entered up to now Begins new xact

Conversely, can ROLLBACK SQL> ROLLBACK; Cancels all statements entered since start of xact

Example: delete from emp; or delete junk;


Direct xact instructions Remember, DDL statements are auto-

committed They cannot be rollbacked

Examples:

Q: Why doesn’t rollback “work”?

drop table junk;rollback;

drop table junk;rollback;

truncate table junk;rollback;

truncate table junk;rollback;


Savepoints Xacts are atomic Can rollback to beginning of current xact

But might want to rollback only part way

Make 10 changes, make one bad change Want to: roll back to before last change

Don’t have Word-like multiple undo But do have savepoints


Savepoints Create a savepoint:

emp example:--changesSAVEPOINT sp1;--changesSAVEPOINT sp2;--changesSAVEPOINT sp3--changesROLLBACK TO sp2;ROLLBACK TO sp1;

--changesSAVEPOINT sp1;--changesSAVEPOINT sp2;--changesSAVEPOINT sp3--changesROLLBACK TO sp2;ROLLBACK TO sp1;

SAVEPOINT savept_name; SAVEPOINT savept_name;

Can skip savepoints But can ROLLBACK

only backwards Can ROLLBACK

only to last COMMIT


AUTOCOMMIT Finally, can turn AUTOCOMMIT on:

SQL> SET AUTOCOMMIT ON;

Then each statement is auto-committed as its own xact Not just DDL statements


New topic: the bulk loader To insert data, can insert rows one at a time

with INSERT INTO <table> VALUES(<>) If data is in/can be computed from other

tables, can use INSERT INTO <table> SELECT …

Often, have text file of data Oracle’s bulk loader will parse file and insert

all into the database


Using the bulk loader The bulk loader takes two files:

The data file The control file, specifying how to load the data

Control file form:

LOAD DATAINFILE <dataFile><APPEND> INTO TABLE <tableName>FIELDS TERMINATED BY '<separator>'(<list of all attribute names to load>)



The control file

Default data file extension: .dat Default control file extension: .ctl If APPEND is omitted, the table must be empty, else

error Attribute list is comma-separated, but order doesn’t

matter Separator can be multi-char




The control file Example control file:

LOAD DATAINFILE test.datINTO TABLE testFIELDS TERMINATED BY '|'(i, s)

LOAD DATAINFILE test.datINTO TABLE testFIELDS TERMINATED BY '|'(i, s)


The data file Plain text file Each line one row in the table Example data file:

1|foo2|bar3| baz

1|foo2|bar3| baz


Running the bulk loader The bulk loader is a command-line program

sqlldr, separate from SQL*Plus:

At cmd line, specify: user/pass (pass is optional here) the control file (which specifies data file), and (optionally) a log file (dft ext: .log) (optionally) a bad file (dft ext: .bad)

c:\ sqlldr scott/tiger control=test log=test bad=badc:\ sqlldr scott/tiger control=test log=test bad=bad


Data in the control file Can also merge the data and control file

(onefile.ctl):

The * indicates that the data is in this file

LOAD DATAINFILE *INTO TABLE testFIELDS TERMINATED BY '|'(i, s)BEGINDATA1|foo2|bar3| baz

LOAD DATAINFILE *INTO TABLE testFIELDS TERMINATED BY '|'(i, s)BEGINDATA1|foo2|bar3| baz


Loading dates In the control file’s attribute list, follow a data

field with a date mask Date masks are case-INsensitive and include:

d - day m - month y - year

withdates.ctl:

LOAD DATAINFILE *INTO TABLE fooFIELDS TERMINATED BY '|'(i, d DATE 'dd-mm-yyyy')BEGINDATA1|01-01-19902|4-1-1998

LOAD DATAINFILE *INTO TABLE fooFIELDS TERMINATED BY '|'(i, d DATE 'dd-mm-yyyy')BEGINDATA1|01-01-19902|4-1-1998


Loading timestamps Similar to dates but includes more chars:

Mi – minutes ss – seconds hh – hour hh24: 24-hour hour ff – millisecond (fractional seconds)

withtimestamps.ctl:

LOAD DATAINFILE *APPEND INTO TABLE tsFIELDS TERMINATED BY ','(s, t timestamp 'yyyymmddhh24miss.ff' )BEGINDATA1,20041012081522.1231,10661012081522.321

LOAD DATAINFILE *APPEND INTO TABLE tsFIELDS TERMINATED BY ','(s, t timestamp 'yyyymmddhh24miss.ff' )BEGINDATA1,20041012081522.1231,10661012081522.321


Loading nulls Two adjacent separators

are interpreted as a null value in the field:

What if null in last field? Two options:

Put TRAILING NULLCOLS following field-term df

Append an extra field sep to end

withnulls.ctl:

3||5|2|41||6||7

3||5|2|41||6||7

LOAD DATAINFILE *APPEND INTO TABLE numsFIELDS TERMINATED BY '|'TRAILING NULLCOLS (a,b,c)BEGINDATA3||5|2|41|2|1|2||

LOAD DATAINFILE *APPEND INTO TABLE numsFIELDS TERMINATED BY '|'TRAILING NULLCOLS (a,b,c)BEGINDATA3||5|2|41|2|1|2||


Lecture 10… regexps

Web apps/security

Data warehousing extensions

XML

OCL3 Oracle 10 g : SQL & PL/SQL Session #9

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