1. M.P. Johnson, DBMS, Stern/NYU, Spring 20081 C20.0046: Database Management Systems Lecture #21 M.P. Johnson Stern School of Business, NYU Spring, 2008

2. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 2 Agenda Stored procedures? Triggers Transactions RAID? Implementation?

3. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 3 Integration with SQL DECLARE l_book_count INTEGER; BEGIN SELECT COUNT(*) INTO l_book_count FROM books WHERE author LIKE '%FEUERSTEIN, STEVEN%'; DBMS_OUTPUT.PUT_LINE ( 'Steven has written (or co-written) ' || l_book_count || ' books.'); END; DECLARE l_book_count INTEGER; BEGIN SELECT COUNT(*) INTO l_book_count FROM books WHERE author LIKE '%FEUERSTEIN, STEVEN%'; DBMS_OUTPUT.PUT_LINE ( 'Steven has written (or co-written) ' || l_book_count || ' books.'); END;

4. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 4 Dynamic PL/SQL E.g.: write function to return number rows in an arbitrary table CREATE OR REPLACE FUNCTION rowCount ( tabname IN VARCHAR2) return integer as retval integer; begin execute immediate 'select count(*) from ' || tabname into retval; return retval; end; / CREATE OR REPLACE FUNCTION rowCount ( tabname IN VARCHAR2) return integer as retval integer; begin execute immediate 'select count(*) from ' || tabname into retval; return retval; end; /

5. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 5 Dynamic PL/SQL for DDL Ordinarily can’t do DDL in PL/SQL But you can in dynamic PL/SQL Here’s an e.g.: CREATE OR REPLACE procedure dropproc(procname in varchar2) as begin execute immediate 'drop procedure ' || procname; end; / CREATE OR REPLACE procedure dropproc(procname in varchar2) as begin execute immediate 'drop procedure ' || procname; end; /

6. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 6 Live examples Factorial function:  http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/ fact.sql http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/ fact.sql Converting between bases:  http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/ numsys.sql http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/ numsys.sql Directory of examples:  http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/ http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/

7. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 7 SPs in MySQL (5.0) Generally similar, though technical diffs  Need to temporarily redefine ; delimiter mysql> drop procedure if exists hello; myslq> delimiter / mysql> create procedure hello() -> begin -> select 'hi'; -> end; -> / mysql> delimiter ; mysql> call hello(); mysql> drop procedure if exists hello; myslq> delimiter / mysql> create procedure hello() -> begin -> select 'hi'; -> end; -> / mysql> delimiter ; mysql> call hello();

8. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 8 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

9. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 9 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.

10. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 10 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

11. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 11 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

12. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 12 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]; 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];

13. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 13 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;

14. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 14 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; 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;

15. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 15 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 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; 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;

16. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 16 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 )... CREATE OR REPLACE TRIGGER valid_when_clause BEFORE INSERT ON frame FOR EACH ROW WHEN ( TO_CHAR(SYSDATE,'HH24') BETWEEN 9 AND 17 )...

17. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 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 UpdateDateTrigger AFTER UPDATE OF data ON R REFERENCING NEW ROW AS NewTuple FOR EACH ROW BEGIN NewTuple.last-modified = sysdate; END; CREATE TRIGGER UpdateDateTrigger AFTER UPDATE OF data ON R REFERENCING NEW ROW AS NewTuple FOR EACH ROW BEGIN NewTuple.last-modified = sysdate; END;

18. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 18 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; 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

19. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 19 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; 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;

20. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 20 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; UPDATE grades SET grade = 'A+' WHERE student_id = 1 AND class_id = 101; DELETE grades WHERE student_id = 2 AND class_id = 101; DELETE grades WHERE student_id = 2 AND class_id = 101;

21. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 21 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; 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;

22. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 22 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; CREATE [OR REPLACE] TRIGGER trigger name {BEFORE | AFTER| {DDL event} ON {DATABASE | SCHEMA} DECLARE Variable declarations BEGIN... some code... END;

23. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 23 DDL trigger e.g. Town crier examples triggered by creates: uninformed_town_crier.sql informed_town_crier.sql

24. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 24 Available DDL events CREATE, ALTER, DROP, GRANT, RENAME, REVOKE, TRUNCATE DDL: any DDL event no_create.sql 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; 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;

25. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 25 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; CREATE [OR REPLACE] TRIGGER trigger name {BEFORE | AFTER} {database event} ON {DATABASE | SCHEMA} DECLARE Variable declarations BEGIN... some code... END;

26. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 26 DB event restrictions Have BEFORE and AFTER as above, but they don’t always apply:  No BEFORE STARTUP/LOGON/SERVERERROR  No AFTER SHUTDOWN/LOGOFF

27. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 27 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; CREATE OR REPLACE TRIGGER on_shutdown BEFORE SHUTDOWN ON DATABASE BEGIN gather_system_stats; END;

28. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 28 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

29. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 29 Default xact behavior (in Oracle) An xact begins upon login By default, xact lasts until logoff  Except for DDL statements  They automatically commit Examples with two views of tbl…  But with TYPE=innodb !  mysql> set autocommit = 0

30. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 30 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;

31. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 31 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;

32. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 32 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

33. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 33 Savepoints Create a savepoint: emp example: --changes SAVEPOINT sp1; --changes SAVEPOINT sp2; --changes SAVEPOINT sp3 --changes ROLLBACK TO SAVEPOINT sp2; ROLLBACK TO SAVEPOINT sp1; --changes SAVEPOINT sp1; --changes SAVEPOINT sp2; --changes SAVEPOINT sp3 --changes ROLLBACK TO SAVEPOINT sp2; ROLLBACK TO SAVEPOINT sp1; SAVEPOINT savept_name; Can skip savepoints But can ROLLBACK only backwards Can ROLLBACK only to last COMMIT

34. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 34 AUTOCOMMIT Finally, can turn AUTOCOMMIT on:  Oralce: SQL> SET AUTOCOMMIT ON;  Mysql: mysql> SET AUTOCOMMIT=1;  Can put this in your config file  Can specify through JDBC, etc. Then each statement is auto-committed as its own xact  Not just DDL statements

35. M.P. Johnson, DBMS, Stern/NYU, Spring 2008 35 RAID levels RAID level 1: each disk gets a mirror RAID level 4: one disk is xor of all others  Each bit is sum mod 2 of corresponding bits E.g.:  Disk 1: 10110011  Disk 2: 10101010  Disk 3: 00111000  Disk 4: How to recover? What’s the disadvantage of R4?  Various other RAID levels in text…