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OCL4 Oracle 10 g : SQL & PL/SQL Session #7

OCL4 Oracle 10 g : SQL & PL/SQL Session #7. 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

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OCL4 Oracle 10 g : SQL & PL/SQL Session #7

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  1. OCL4 Oracle 10g:SQL & PL/SQLSession #7 Matthew P. Johnson CISDD, CUNY June, 2005 Matthew P. Johnson, OCL4, CISDD CUNY, Sept 2005

  2. Agenda • Triggers • Transactions • Oracle’s bulk loader • Go over some labs • Do some more labs Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

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

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

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

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

  7. Trigger form 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]; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  8. Trigger type examples • First run copy_tables.sql • statement_vs_row.sql • INSERT INTO to_table SELECT * FROM from_table; • before_vs_after.sql • INSERT INTO to_table SELECT * FROM from_table; • one_trigger_per_type.sql • INSERT INTO to_table VALUES (1); UPDATE to_table SET col1 = 10; DELETE to_table; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  9. 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 ROW BEGIN check_age (:NEW.date_of_birth); check_resume (:NEW.resume); END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  10. Triggers with WHEN CREATE OR REPLACE TRIGGER check_raise AFTER UPDATE OF salary, commission ON employee FOR EACH ROW WHEN ((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; • NB: WHEN applies only to row-level triggers Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  11. 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_clause BEFORE INSERT ON frame FOR EACH ROW WHEN ( TO_CHAR(SYSDATE,'HH24') BETWEEN 9 AND 17 ) ... Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  12. 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 UpdateDateTrigger AFTER UPDATE OF data ON R REFERENCING NEW ROW AS NewTuple FOR EACH ROW BEGIN NewTuple.last-modified = sysdate; END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  13. Multiple DML actions • DML actions may be ORed together CREATE OR REPLACE TRIGGER three_for_the_price_of_one BEFORE DELETE OR INSERT OR UPDATE ON account_transaction FOR EACH ROW BEGIN IF 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 Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  14. More on UPDATING • UPDATING may be called for partic. columns CREATE OR REPLACE TRIGGER validate_update BEFORE UPDATE ON account_transaction FOR EACH ROW BEGIN IF UPDATING ('ACCOUNT_NO') THEN errpkg.raise('Account number cannot be updated'); END IF; END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  15. Extended auditing example • Tables: grades, grades_audit • Run: grades_tables.sql, grades_audit.sql • Cases: hacker changes grades, deletes others UPDATE grades SET grade = 'A+' WHERE student_id = 1 AND class_id = 101; DELETE grades WHERE student_id = 2 AND class_id = 101; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  16. Extended auditing example • Run: grades_tables.sql, grades_audit2.sql • Cases: hacker changes student or class ids UPDATE grades SET student_id = 3 WHERE student_id = 1 AND class_id = 101; UPDATE grades SET student_id = 1 WHERE student_id = 2 AND class_id = 101; UPDATE grades SET student_id = 2 WHERE student_id = 3 AND class_id = 101; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  17. 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 declarations BEGIN ... some code... END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  18. DDL trigger e.g. • Town crier examples triggered by creates: • uninformed_town_crier.sql • informed_town_crier.sql Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  19. 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 SCHEMA BEGIN RAISE_APPLICATION_ERROR (-20000, 'ERROR : Objects cannot be created in the production database.'); END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  20. 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 declarations BEGIN ... some code... END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  21. DB event restrictions • Have BEFORE and AFTER as above, but they don’t always apply: • No BEFORESTARTUP/LOGON/SERVERERROR • No AFTERSHUTDOWN/LOGOFF Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  22. DB Trigger e.g. • Gather stats before shutdown: • Log error messages CREATE OR REPLACE TRIGGER on_shutdown BEFORE SHUTDOWN ON DATABASE BEGIN gather_system_stats; END; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  23. 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'; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

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

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

  26. Intermission • Go over previous labs • Begin lab… • Break Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

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

  28. 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… Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  29. 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; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  30. Direct xact instructions • Remember, DDL statements are auto-committed •  They cannot be rollbacked • Examples: • Q: Why doesn’t rollback “work”? drop table junk; rollback; truncate table junk; rollback; Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

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

  32. Savepoints • Create a savepoint: • emp example: SAVEPOINT savept_name; --changes SAVEPOINT sp1; --changes SAVEPOINT sp2; --changes SAVEPOINT sp3 --changes ROLLBACK TO sp2; ROLLBACK TO sp1; • Can skip savepoints • But can ROLLBACK only backwards • Can ROLLBACK only to last COMMIT Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  33. AUTOCOMMIT • Finally, can turn AUTOCOMMIT on: • SQL> SET AUTOCOMMIT ON; • Then each statement is auto-committed as its own xact • Not just DDL statements Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

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

  35. 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 DATA INFILE <dataFile> <APPEND> INTO TABLE <tableName> FIELDS TERMINATED BY '<separator>' (<list of all attribute names to load>) Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  36. 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 LOAD DATA INFILE <dataFile> <APPEND> INTO TABLE <tableName> FIELDS TERMINATED BY '<separator>' (<list of all attribute names to load>) Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  37. The control file • Example control file: LOAD DATA INFILE test.dat INTO TABLE test FIELDS TERMINATED BY '|' (i, s) Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  38. The data file • Plain text file • Each line  one row in the table • Example data file: 1|foo 2|bar 3| baz Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  39. 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=bad Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  40. 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 DATA INFILE * INTO TABLE test FIELDS TERMINATED BY '|' (i, s) BEGINDATA 1|foo 2|bar 3| baz Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  41. 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 DATA INFILE * INTO TABLE foo FIELDS TERMINATED BY '|' (i, d DATE 'dd-mm-yyyy') BEGINDATA 1|01-01-1990 2|4-1-1998 Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  42. 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 DATA INFILE * APPEND INTO TABLE ts FIELDS TERMINATED BY ',' (s, t timestamp 'yyyymmddhh24miss.ff' ) BEGINDATA 1,20041012081522.123 1,10661012081522.321 Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  43. Loading nulls 3||5 |2|4 1||6 ||7 • 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: LOAD DATA INFILE * APPEND INTO TABLE nums FIELDS TERMINATED BY '|' TRAILING NULLCOLS (a,b,c) BEGINDATA 3||5 |2|4 1|2| 1|2|| Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

  44. Lecture 8… • regexps • Web apps/security • XML • Data warehousing extensions Matthew P. Johnson, OCL3, CISDD CUNY, June 2005

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