1 Moving a Java Program into a Database

2 Motivation We would like to be able to run a Java program from within Oracle. This will allow us to: –call a Java function inside a query –call a Java function inside a trigger (triggers will be explained later on…)

3 Basic Procedure 1.Create a Java program. Make the function that we want to use static. 2.Load the Java program into the database. 3.Create a PL/SQL procedure that will wrap the Java function 4.Call the PL/SQL procedure. We learn each step in detail…

4 Hello World - Java CREATE OR REPLACE AND COMPILE JAVA SOURCE NAMED "Hello" AS public class Hello { public static void sayHello(String name) { System.out.println("Hello World, " + name); } public static String returnHello(String name) { return "Hello World, " + name; } }; /

5 Hello World – PL/SQL (1) CREATE OR REPLACE PROCEDURE say_hello(name VARCHAR2) as LANGUAGE JAVA NAME 'Hello.sayHello(java.lang.String)'; / Note: Errors in creating a procedure can be seen with the command: show errors

6 Calling say_hello SET SERVEROUTPUT ON SIZE CALL DBMS_JAVA.SET_OUTPUT ( ); CALL say_hello( ‘ Sara ’ ); We will see: “Hello World, Sara” on the screen.

7 Hello World – PL/SQL CREATE OR REPLACE FUNCTION return_hello(name VARCHAR2) return VARCHAR2 as LANGUAGE JAVA NAME 'Hello.returnHello(java.lang.String) return java.lang.String'; /

8 Calling return_hello SELECT return_hello( ‘ Sara ’ ) FROM DUAL; We will see: RETURNHELLO('SARA') Hello World, Sara

9 Notes Java programs can also be loaded using the utility loadjava. Details will be given when necessary. It may be necessary sometimes to recompile a procedure or a java source. This can be done by: –alter procedure say_hello compile; –alter java source “Hello” compile; Note the need to use quotes around Java source names, since Java is case sensitive.

10 Moving Program Logic into the Database: Triggers

11 What is a Trigger? A trigger is a procedure that is automatically called when certain events occur in the database. Triggers can be made to run when rows are inserted, deleted or updated. Triggers can be run before or after the action. Triggers can be run once per statement or once per row affected.

12 General Form of a Trigger CREATE [or REPLACE] TRIGGER trig_name {BEFORE | AFTER | INSTEAD OF} {DELETE | INSERT | UPDATE [of column [, column]...] } [or {DELETE | INSERT | UPDATE [of column [, column]...] }...] on {table_name | view_name} FOR EACH {ROW | STATEMENT} [WHEN (condition)] PL/SQL block

13 Backing Up Data CREATE TRIGGER backup_sailors_trig AFTER UPDATE of Rating on Sailors FOR EACH ROW WHEN (old.rating < new.rating) BEGIN INSERT INTO Sailors_Backup VALUES (:old.sid, :old.sname, :old:age, :old:rating); END / Why AFTER?

14 Ensuring Upper Case CREATE TRIGGER upper_case_program_type_trig BEFORE INSERT or UPDATE on Program FOR EACH ROW BEGIN :new.type := UPPER(:new.type); END / Why BEFORE?

15 Calling a Procedure CREATE TRIGGER notify_ta_trig AFTER INSERT or UPDATE or DELETE on Db_Grades FOR EACH STATEMENT WHEN(User <> ‘ db ’ ) BEGIN call send (User || ‘ trying to access table Db_Grades ’ ); END /

16 Views and Triggers

17 Changing a Table through a View (1) If a view is based on a single table you can insert, update and delete rows from the table through the view under the following conditions: –You can’t insert if the underlying table has non null columns not appearing in the view –You can’t insert or update if any of the view columns referenced in the command contains functions or calculations

18 Changing a Table through a View (2) –You can’t insert, update or delete if the view contains group by or distinct.

19 Inserting Allowed CREATE VIEW OldSailors as SELECT * FROM Sailors WHERE age > 50; INSERT INTO OldSailors(sid,sname,age,rating) VALUES(12, ‘ Joe ’,51,10); INSERT INTO OldSailors(sid,sname,age,rating) VALUES(12, ‘ Mary ’,49,10);

20 Inserting Not Allowed CREATE VIEW SailorsInfo as SELECT sname, rating FROM Sailors WHERE age>50; INSERT INTO SailorsInfo VALUES( ‘ Joe ’,10); Illegal!

21 Updating Allowed CREATE VIEW SailorsInfo as SELECT sname, rating FROM Sailors WHERE age>50; UPDATE SailorsInfo SET rating = 6 WHERE sname = ‘ Joe ’ ; UPDATE Sailors SET rating = 6 WHERE sname = ‘ Joe ’ and age>50;

22 Updating Not Allowed CREATE VIEW SailorsInfo2 as SELECT sname, rating + age as ra FROM Sailors WHERE age>50; UPDATE SailorsInfo2 SET ra = 7 WHERE sname = ‘ Joe ’ ; Illegal!

23 Deleting Allowed CREATE VIEW SailorsInfo2 as SELECT sname, rating + age as ra FROM Sailors WHERE age>50; DELETE FROM SailorsInfo2 WHERE sname = ‘ Joe ’ and ra = 56; DELETE FROM Sailors WHERE sname = ‘ Joe ’ and (rating + age) >50 and age > 50;

24 Some More Examples: What will these commands do? UPDATE OldSailors SET rating = 10; DELETE FROM OldSailors; UPDATE OldSailors SET age = age +1 WHERE age <= 50;

25 Using a Views with Triggers Consider the relation: All_Favorites(url, login) This table stores the favorite web sites of CS students. Two views have been created over this table: User_Favorites: The favorites of current user Anon_Favorites: All the favorites, but without stud_id, to preserve anonymity.

26 The Views CREATE View User_Favorites as SELECT url FROM All_Favorites WHERE login = user; CREATE View Anon_Favorites as SELECT url FROM All_Favorites;

27 Inserting New URLs The table All_Favorites can not be inserted into directly by a student because the privileges are lacking The views can’t be inserted through, since login is a non null column CREATE TRIGGER insert_url INSTEAD of INSERT on User_Favorites for each row begin insert into All_Favorites(url, login) values(User,:new.url); end;

28 Using Triggers to Manipulate Complex Views Oracle can sometimes insert through a view based on several tables. Oracle can’t insert into multiple tables through a view. CREATE VIEW SailorsReserves as SELECT S.sid, sname, rating, age, bid, date FROM Sailors S, Reserves R WHERE S.sid = R.sid;

29 Inserting into a Complex View: Won’t Work This won’t work, since we are attempting to insert into 2 tables. In addition, we are not specifying a value for the sid field of Reserves, which is part of the key! INSERT INTO SailorsReserves(sid,sname,rating,age,bid,date) VALUES (1, ’ Joe ’, 10, 50, 103, ’ ’ );

30 Using a Trigger to Insert CREATE TRIGGER insert_sailors_reserves_trig INSTEAD of INSERT on SailorsReserves for each row begin insert into Sailors(sid, sname, rating, age) values(:new.sid, :new.sname, :new.rating, :new.age); insert into Reserves(sid, bid, date) values(:new.sid, :new.bid, :new.date); end;

31 Materialized Views

32 What and Why? What: A materialized view is a view that actually exists as a table Why: This can be more efficient than re- computing the view’s query each time it is accessed Problem: How is the materialized view kept up to date when the underlying tables are changed? Note: We will just see the ideas here and not the syntax

33 Simple vs. Complex A Simple Materialized View: 1.Selects rows from only 1 table 2.Does not perform set operations, joins or group bys Otherwise, it is a Complex Materialized View.

34 Options for Materialized Views Refresh mode, one of –Fast (only possible for Simple Materialized Views): add minimal changes –Complete: Recompute the query –Force: Fast, if possible; otherwise complete When is refresh performed? –On demand: When refresh is specifically asked for –On commit: When underlying table has changed

35 Fast Refresh Consider a materialized view defined by the query: SELECT sname, age FROM Sailors WHERE rating 50;

36 Fast Refresh INSERT INTO Sailors(sid,sname,rating,age) VALUES (12, ’ Joe ’,8,52); How would the view be updated when the following commands are performed? DELETE FROM Sailors WHERE age < 54; UPDATE Sailors SET age = age - 1 WHERE rating > 10;

37 More Options Query Rewrite: Can a materialized view be used instead of a table in a query? Suppose we had the view defined before, and we wanted to compute the query: SELECT age FROM Sailors WHERE age > 51 and age < 85;