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Database Systems SQL Queries, PL/SQL, Triggers Gergely Czuczy Cause Light Wounds: I call upon chaos to cause unbalanced parentheses.

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Presentation on theme: "Database Systems SQL Queries, PL/SQL, Triggers Gergely Czuczy Cause Light Wounds: I call upon chaos to cause unbalanced parentheses."— Presentation transcript:

1 Database Systems SQL Queries, PL/SQL, Triggers Gergely Czuczy Cause Light Wounds: I call upon chaos to cause unbalanced parentheses.

2 Todays Database FIRST, run this script: _AFTER_ the first, run this one:

3 (NOT) EXISTS You can satisfy queries where you have to select things which are related to all other things. For an example select those pilots who know all the planes.

4 (NOT) EXISTS First, select all the planes(q1). From q1 subtract the planes that the actual pilot knows(q2) You will get of a set of planes from q2. We have to select those pilots where this set is empty.

5 (NOT) EXISTS SELECT p1.name FROM pilots p1 WHERE NOT EXISTS ( (SELECT id FROM planes) MINUS (SELECT k1.planeid FROM knows k1 WHERE k1.pilotid = p1.id) ) ;

6 PL/SQL With PL/SQL you will be able to do many jobs in oracle that require programming, such as writing triggers, functions, and so on. In a PL/SQL block you can use queries such in anywhere else.

7 PL/SQL The PL/SQL block: DECLARE BEGIN END

8 PL/SQL Declaring variables: Right after the DECLARE keyword ; Example: emp_name varchar2(1024); current date; nextid integer;

9 PL/SQL IF-statements: IF THEN ELSIF THEN END IF; The ELSIF branch is optional

10 Trigger A trigger executes a procedure for some kind of action. For an example on every INSERT statement on a table a trigger executed that logs the newly inserted row. Triggers can be fired before or after some kind of action

11 Trigger + PL/SQL Triggers are mostly written in PL/SQL Special variables that you can use: –NEW: the newly inserted row’s data, or the updated data in an UPDATE query –OLD: the old data in a DELETE/UPDATE trigger Where refering to NEW/OLD you have to prefix it by a ‘:’, ex: :NEW.personid

12 Trigger Example #1 CREATE OR REPLACE TRIGGER trg_knows BEFORE DELETE OR INSERT ON knows FOR EACH ROW DECLARE BEGIN IF INSERTING THEN INSERT INTO logs (systime,action) VALUES (sysdate,:NEW.pilotid||' has learned plane '||:NEW.planeid); ELSIF DELETING THEN INSERT INTO logs (systime,action) VALUES (sysdate,:NEW.pilotid||' has forgotten plane '||:NEW.planeid); END IF; END;

13 Trigger Example #2 CREATE OR REPLACE TRIGGER trg_knows_update BEFORE UPDATE ON knows FOR EACH ROW DECLARE BEGIN :NEW.pilotid := :OLD.pilotid; :NEW.planeid := :OLD.planeid; END;

14 Sequence A sequence stores a value that can be incremented by a function call. It’s useful for automagicaly creating ID’s. To create a sequence use: CREATE SEQUENCE some_seq; To get the next value use: some_seq.nextval();

15 Exercise Implement a trigger in your project!

16 Have a nice weekend!


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