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

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

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

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

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

M.P. Johnson, DBMS, Stern/NYU, Spring Live examples Factorial function:  fact.sql fact.sql Converting between bases:  numsys.sql numsys.sql Directory of examples: 

M.P. Johnson, DBMS, Stern/NYU, Spring 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();

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

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

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

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

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

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

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

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

M.P. Johnson, DBMS, Stern/NYU, Spring 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 )...

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

M.P. Johnson, DBMS, Stern/NYU, Spring 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:  Disk 2:  Disk 3:  Disk 4: How to recover? What’s the disadvantage of R4?  Various other RAID levels in text…