M.P. Johnson, DBMS, Stern/NYU, Spring 20051 C20.0046: Database Management Systems Lecture #19 M.P. Johnson Stern School of Business, NYU Spring, 2005.

M.P. Johnson, DBMS, Stern/NYU, Spring 20051 C20.0046: Database Management Systems Lecture #19 M.P. Johnson Stern School of Business, NYU Spring, 2005

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 2 Homework Project part 3 due today Project part 4 up soon… Topic: populating your tables with data  Using MySQL’s bulk loader Can get errors parsing  Start early!

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 3 NYU Infrastructure News The Oracle client should be working as usual again Can run sqlplus and Pro*C programs without touching TWO_TASK

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 4 Agenda: Programming for SQL Embedded SQL  Pro*C, SQLJ CLI  SQL/CLI in C  JDBC in Java  DBI/DBDs in Perl, PHP Stored Procedures:  PL/SQL, Triggers MySQL Bulk Loader

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 5 Goals 1. Have more confidence in writing scripts/functions/procedures Be able to respond to ftn/proc errors 2. Be able to define a simple trigger So code executes at the right time 3. Understand how to load a text file of records into MySQL

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 6 PL/SQL “Procedural Language for SQL”  Oracle’s language for stored procedures Simple, interpreted, procedural language But Pascal-like:  BEGIN END, not { }  AND OR, not && ||  vars defined at top of procedre  how return works

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 7 Hello, World Try again… SET SERVEROUTPUT ON BEGIN -- print out message DBMS_OUTPUT.PUT_LINE('Hello World, from PL/SQL'); END; / SET SERVEROUTPUT ON BEGIN -- print out message DBMS_OUTPUT.PUT_LINE('Hello World, from PL/SQL'); END; /

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 8 Example procedure Define the procedure: Now we can call it: CREATE PROCEDURE testProcedure AS BEGIN INSERT INTO Student VALUES (5, ‘Godel'); END; CREATE PROCEDURE testProcedure AS BEGIN INSERT INTO Student VALUES (5, ‘Godel'); END; EXEC testProcedure

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 9 Procedure I/O example A procedure to take a beer and price and add it to Joe's menu: Sells(bar, beer, price) CREATE PROCEDURE izzyMenu( b IN Sells.beer%TYPE, p IN Sells.price%TYPE) AS BEGIN INSERT INTO Sells VALUES(‘Izzy’’s', b, p); END; / CREATE PROCEDURE izzyMenu( b IN Sells.beer%TYPE, p IN Sells.price%TYPE) AS BEGIN INSERT INTO Sells VALUES(‘Izzy’’s', b, p); END; /

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 10 Function example http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec19/maxval.sql CREATE OR REPLACE FUNCTION maxval(a IN int, b IN int) RETURN int AS BEGIN IF a > b THEN RETURN a; ELSE RETURN b; END IF; END maxval; CREATE OR REPLACE FUNCTION maxval(a IN int, b IN int) RETURN int AS BEGIN IF a > b THEN RETURN a; ELSE RETURN b; END IF; END maxval; INSERT INTO R VALUES(“abc”, maxval(5,10));

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 11 Word count program CREATE OR REPLACE FUNCTION wordcount (str IN VARCHAR2) RETURN PLS_INTEGER AS /* words PLS_INTEGER := 0; ***Commented out for intentional error*** */ len PLS_INTEGER := NVL(LENGTH(str),0); inside_a_word BOOLEAN; BEGIN FOR i IN 1..len + 1 LOOP IF ASCII(SUBSTR(str, i, 1)) len THEN IF inside_a_word THEN words := words + 1; inside_a_word := FALSE; END IF; ELSE inside_a_word := TRUE; END IF; END LOOP; RETURN words; END; CREATE OR REPLACE FUNCTION wordcount (str IN VARCHAR2) RETURN PLS_INTEGER AS /* words PLS_INTEGER := 0; ***Commented out for intentional error*** */ len PLS_INTEGER := NVL(LENGTH(str),0); inside_a_word BOOLEAN; BEGIN FOR i IN 1..len + 1 LOOP IF ASCII(SUBSTR(str, i, 1)) len THEN IF inside_a_word THEN words := words + 1; inside_a_word := FALSE; END IF; ELSE inside_a_word := TRUE; END IF; END LOOP; RETURN words; END; http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/wordcount.sql

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 12 Getting errors Simple says: To get actual errors, say SHOW ERR(ORS) Can also get errors per object: Warning: must get object type right! Can also look at user_errors tbl directly Warning: Function created with compilation errors. SQL> show errors function wordcount

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 13 Stored ftns & procs persist Once a function or procedure is created, it persists until it’s dropped Stored procs are stored in the DB itself  In user_procedures in Oracle Also, can describe ftns and procs: CREATE OR REPLACE FUNCTION … SELECT object_name from user_procedures; SQL> describe wordcount

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 14 Calling functions and procedures Procedures can simple executed, ftns can’t How to just call a ftn? 1. Can use dbms_output, as seen 2. Can also select the ftn value from dual SQL> select(wordcount(‘hi there’) from dual;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 15 Programs and rights By default, only the creator of a program may run it (apart from the admin) If others should run, must GRANT them permission: Permissions can be revoked: Can also grant to particular roles or everyone: Wider/narrower grant ops are independent… SQL> GRANT EXECUTE ON wordcount TO george; SQL> REVOKE EXECUTE FROM wordcount TO george; SQL> GRANT EXECUTE ON wordcount TO everyone;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 16 Branching IF–THEN statements use THEN Must end with END IF Use ELSIF in place of ELSE IF Example:  http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec19/maxval.sql http://pages.stern.nyu.edu/~mjohnson/dbms/eg/lec19/maxval.sql IF THEN ELSIF END IF; IF THEN ELSIF END IF;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 17 More ifs IF ELSE END IF; IF ELSE END IF; IF ELSEIF ELSE END IF; IF ELSEIF ELSE END IF;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 18 Multiple elsifs An if statement can have multiple elseifs: IF salary >= 10000 AND salary <= 20000 THEN give_bonus(employee_id, 1500); ELSIF salary > 20000 AND salary <= 40000 THEN give_bonus(employee_id, 1000); ELSIF salary > 40000 THEN give_bonus(employee_id, 400); END IF; IF salary >= 10000 AND salary <= 20000 THEN give_bonus(employee_id, 1500); ELSIF salary > 20000 AND salary <= 40000 THEN give_bonus(employee_id, 1000); ELSIF salary > 40000 THEN give_bonus(employee_id, 400); END IF;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 19 Loop example DECLARE i NUMBER := 1; BEGIN LOOP INSERT INTO T1 VALUES(i,i); i := i+1; EXIT WHEN i>100; END LOOP; END; / DECLARE i NUMBER := 1; BEGIN LOOP INSERT INTO T1 VALUES(i,i); i := i+1; EXIT WHEN i>100; END LOOP; END; /

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 20 More loops Infinite loop: while loop: LOOP executable_statements; END LOOP; LOOP executable_statements; END LOOP; WHILE condition LOOP executable_statements; END LOOP; WHILE condition LOOP executable_statements; END LOOP;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 21 For loops Integer for loop: Cursor for loop: FOR for_index IN low_value.. high_value LOOP executable_statements; END LOOP; FOR for_index IN low_value.. high_value LOOP executable_statements; END LOOP; FOR record_index IN my_cursor LOOP executable_statements; END LOOP; FOR record_index IN my_cursor LOOP executable_statements; END LOOP;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 22 For loop example Example:  http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/for.sql http://pages.stern.nyu.edu/~mjohnson/dbms/plsql/for.sql FOR my-rec IN my-cursor LOOP … END LOOP; FOR my-rec IN my-cursor LOOP … END LOOP;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 23 PL/SQL v. SQL There are some things SQL can’t do (e.g., factorial), but some problems can be solved in both DECLARE CURSOR checked_out_cur IS SELECT pet_id, name, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; BEGIN FOR checked_out_rec IN checked_out_cur LOOP INSERT INTO occupancy_history (pet_id, name, checkout_date) VALUES (checked_out_rec.pet_id, checked_out_rec.name, checked_out_rec.checkout_date); DELETE FROM occupancy WHERE pet_id = checked_out_rec.pet_id; END LOOP; END; DECLARE CURSOR checked_out_cur IS SELECT pet_id, name, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; BEGIN FOR checked_out_rec IN checked_out_cur LOOP INSERT INTO occupancy_history (pet_id, name, checkout_date) VALUES (checked_out_rec.pet_id, checked_out_rec.name, checked_out_rec.checkout_date); DELETE FROM occupancy WHERE pet_id = checked_out_rec.pet_id; END LOOP; END;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 24 PL/SQL v. SQL The same thing can be done w/o a cursor: BEGIN INSERT INTO occupancy_history (pet_id, NAME, checkout_date) SELECT pet_id, NAME, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; DELETE FROM occupancy WHERE checkout_date IS NOT NULL; END; BEGIN INSERT INTO occupancy_history (pet_id, NAME, checkout_date) SELECT pet_id, NAME, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; DELETE FROM occupancy WHERE checkout_date IS NOT NULL; END;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 25 Dynamic PL/SQL Saw “dynamic SQL” in the cases of Pro*C and JDBC  Ability to run ad-hoc (non-hard-coded) SQL in programs/scripts Can also do this in PL/SQL The string can be passed in, created from concatenation, etc. EXECUTE IMMEDIATE ;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 26 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 2005 27 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 2005 28 More on PL/SQL O’Reilly’s Oracle PL/SQL Programming:  http://www.unix.org.ua/orelly/oracle/prog2/ http://www.unix.org.ua/orelly/oracle/prog2/  This lecture somewhat follows 3 rd edition of this book PL/SQL Reference & Tutorial:  http://www.ilook.fsnet.co.uk/ora_sql/sqlmain2.htm http://www.ilook.fsnet.co.uk/ora_sql/sqlmain2.htm Introduction to PL/SQL:  http://www.geocities.com/cliktoprogram/plsql/introduction.html http://www.geocities.com/cliktoprogram/plsql/introduction.html Oracle FAQ's Script and Code Exchange:  http://www.orafaq.com/scripts/ http://www.orafaq.com/scripts/

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 29 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/

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 30 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 2005 31 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 2005 32 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 2005 33 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 2005 34 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 2005 35 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; Skip to: Extended auditing example

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 36 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 2005 37 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 2005 38 Triggers with WHEN Remember: WHEN applies only to row-levels 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 2005 39 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 2005 40 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 2005 41 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 2005 42 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 2005 43 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 2005 44 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 2005 45 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; 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; Skip to: the bulk loader

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 46 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 2005 47 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 2005 48 DB Trigger e.g. Gather stat before shutdown: Log error messages: error_log.sql 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 2005 49 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';

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 50 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

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 51 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

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 52 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 BEFORE UPDATE OF data ON R REFERENCING NEW ROW AS NewTuple FOR EACH STATEMENT BEGIN NewTuple.last-modified = sysdate; END; CREATE TRIGGER UpdateDateTrigger BEFORE UPDATE OF data ON R REFERENCING NEW ROW AS NewTuple FOR EACH STATEMENT BEGIN NewTuple.last-modified = sysdate; END;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 53 Triggers: Row-level example MovieExec(name, address, cert#, netWorth) “If someone decreases a movie executive’s net worth, I want the database to reset itself to the previous net worth.” CREATE TRIGGER NetWorthTrigger AFTER UPDATE OF netWorth ON MovieExec REFERENCING NEW ROW AS NewTuple OLD ROW AS OldTuple FOR EACH ROW WHEN (OldTuple.netWorth>NewTuple.netWorth) UPDATE MovieExec SET netWorth = oldTuple.netWorth WHERE cert# = newTuple.cert#) CREATE TRIGGER NetWorthTrigger AFTER UPDATE OF netWorth ON MovieExec REFERENCING NEW ROW AS NewTuple OLD ROW AS OldTuple FOR EACH ROW WHEN (OldTuple.netWorth>NewTuple.netWorth) UPDATE MovieExec SET netWorth = oldTuple.netWorth WHERE cert# = newTuple.cert#)

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 54 Triggers: Table-level example MovieExec(name, address, cert#, netWorth) “If someone updates the net worth of one movie exec so that the average net worth of all movie execs becomes less than $50,000, I want the database to reset itself.” CREATE TRIGGER AvgNetWorthTrigger AFTER UPDATE OF netWorth ON MovieExec REFERENCING OLD TABLE AS OldStuff, NEW TABLE AS NewStuff FOR EACH STATEMENT WHEN (50000 > (SELECT AVG(netWorth) FROM MovieExec)) BEGIN DELETE FROM MovieExec WHERE (Name, address, cert#, netWorth) IN NewStuff; INSERT INTO MovieExec (SELECT * FROM OldStuff); END; CREATE TRIGGER AvgNetWorthTrigger AFTER UPDATE OF netWorth ON MovieExec REFERENCING OLD TABLE AS OldStuff, NEW TABLE AS NewStuff FOR EACH STATEMENT WHEN (50000 > (SELECT AVG(netWorth) FROM MovieExec)) BEGIN DELETE FROM MovieExec WHERE (Name, address, cert#, netWorth) IN NewStuff; INSERT INTO MovieExec (SELECT * FROM OldStuff); END;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 55 Mutating Table Errors It’s generally impossible to a row-level trigger to modify or query the table that triggered it   trigger 2 slides back is not allowed! Does not apply to statement-level triggers   trigger 1 slide back is Can do the equiv by creating a complicated statement-level trigger Won’t discuss…

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 56 New topic: the bulk loader To insert data, can insert rows one at a time with INSERT INTO VALUES(<>) If data is in/can be computed from other tables, can use  INSERT INTO SELECT … Often, have text file of data MySQL’s bulk loader will parse file and insert all into the database

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 57 Using the bulk loader Use mysqlimport command  Takes a text file as input  Each line ~ 1 row  Tab-delimited 100 Max Sydow 101 Count Dracula 100 Max Sydow 101 Count Dracula

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 58 Running the bulk loader The bulk loader is a command-line program mysqlimport, separate from SQL*Plus: At cmd line, specify:  user/pass (pass is optional here)  Host  Database  Input file / table name sales% mysqlimport -hmysql2 -umy- NetID -p --local my-db imptest.txt http://pages.stern.nyu.edu/~mjohnson/dbms/proj4.html

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 59 IMPORT DATA command Can also load data while inside mysql: Does not work without LOCAL  Means: reading from client (your directory), not server mysql> LOAD DATA LOCAL INFILE 'imptest.txt' INTO TABLE imptest;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 60 More info If you want, you can  Use a different field separator  Reorder the fields  Import date values For more info, see the webpages:  http://dev.mysql.com/doc/mysql/en/mysqlimport.ht ml http://dev.mysql.com/doc/mysql/en/mysqlimport.ht ml  http://dev.mysql.com/doc/mysql/en/load-data.html http://dev.mysql.com/doc/mysql/en/load-data.html

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 61 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 2005 62 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…

M.P. Johnson, DBMS, Stern/NYU, Spring 2005 63 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 2005 64 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 2005 65 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 2005 66 Savepoints Create a savepoint: emp example: --changes SAVEPOINT sp1; --changes SAVEPOINT sp2; --changes SAVEPOINT sp3 --changes ROLLBACK TO sp2; ROLLBACK TO sp1; --changes SAVEPOINT sp1; --changes SAVEPOINT sp2; --changes SAVEPOINT sp3 --changes ROLLBACK TO sp2; ROLLBACK TO 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 2005 67 AUTOCOMMIT Finally, can turn AUTOCOMMIT on:  SQL> SET AUTOCOMMIT ON; Then each statement is auto-committed as its own xact  Not just DDL statements

M.P. Johnson, DBMS, Stern/NYU, Spring 20051 C20.0046: Database Management Systems Lecture #19 M.P. Johnson Stern School of Business, NYU Spring, 2005.

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M.P. Johnson, DBMS, Stern/NYU, Spring 20051 C20.0046: Database Management Systems Lecture #19 M.P. Johnson Stern School of Business, NYU Spring, 2005.

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Presentation on theme: "M.P. Johnson, DBMS, Stern/NYU, Spring 20051 C20.0046: Database Management Systems Lecture #19 M.P. Johnson Stern School of Business, NYU Spring, 2005."— Presentation transcript:

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