Mega Code Archive

Trigger Which Modifies a Mutating Table

SQL> SQL> CREATE TABLE lecturer ( 2 id NUMBER(5) PRIMARY KEY, 3 first_name VARCHAR2(20), 4 last_name VARCHAR2(20), 5 major VARCHAR2(30), 6 current_credits NUMBER(3) 7 ); Table created. SQL> SQL> SQL> SQL> CREATE OR REPLACE TRIGGER LimitMajors 2 BEFORE INSERT OR UPDATE OF major ON lecturer 3 FOR EACH ROW 4 DECLARE 5 studentMax CONSTANT NUMBER := 5; 6 studentCount NUMBER; 7 BEGIN 8 SELECT COUNT(*) 9 INTO studentCount 10 FROM lecturer 11 WHERE major = :new.major; 12 13 IF studentCount + 1 > studentMax THEN 14 RAISE_APPLICATION_ERROR(-20000, 15 'Too many lecturer in major ' || :new.major); 16 END IF; 17 END LimitMajors; 18 / Trigger created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10001, 'Scott', 'Lawson','Computer Science', 11); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major, current_credits) 2 VALUES (10002, 'Mar', 'Wells','History', 4); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10003, 'Jone', 'Bliss','Computer Science', 8); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10004, 'Man', 'Kyte','Economics', 8); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10005, 'Pat', 'Poll','History', 4); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10006, 'Tim', 'Viper','History', 4); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10007, 'Barbara', 'Blues','Economics', 7); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10008, 'David', 'Large','Music', 4); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10009, 'Chris', 'Elegant','Nutrition', 8); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10010, 'Rose', 'Bond','Music', 7); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10011, 'Rita', 'Johnson','Nutrition', 8); 1 row created. SQL> SQL> INSERT INTO lecturer (id, first_name, last_name, major,current_credits) 2 VALUES (10012, 'Sharon', 'Clear','Computer Science', 3); 1 row created. SQL> SQL> SQL> drop table lecturer; Table dropped.