Mega Code Archive

This is an example of a DML trigger

SQL> SQL> CREATE TABLE major_stats ( 2 major VARCHAR2(30), 3 total_credits NUMBER, 4 total_students NUMBER); Table created. SQL> SQL> INSERT INTO major_stats (major, total_credits, total_students) VALUES ('Computer Science', 22, 3); 1 row created. SQL> SQL> INSERT INTO major_stats (major, total_credits, total_students) VALUES ('History', 12, 3); 1 row created. SQL> SQL> INSERT INTO major_stats (major, total_credits, total_students) VALUES ('Economics', 15, 2); 1 row created. SQL> SQL> INSERT INTO major_stats (major, total_credits, total_students) VALUES ('Music', 11, 2); 1 row created. SQL> SQL> INSERT INTO major_stats (major, total_credits, total_students) VALUES ('Nutrition', 16, 2); 1 row created. SQL> SQL> SQL> CREATE TABLE students ( 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> CREATE OR REPLACE TRIGGER UpdateMajorStats 2 AFTER INSERT OR DELETE OR UPDATE ON students 3 DECLARE 4 CURSOR c_Statistics IS 5 SELECT major, COUNT(*) total_students, 6 SUM(current_credits) total_credits 7 FROM students 8 GROUP BY major; 9 BEGIN 10 DELETE FROM major_stats; 11 12 FOR v_StatsRecord in c_Statistics LOOP 13 INSERT INTO major_stats (major, total_credits, total_students) 14 VALUES (v_StatsRecord.major, v_StatsRecord.total_credits, 15 v_StatsRecord.total_students); 16 END LOOP; 17 END UpdateMajorStats; 18 / Trigger created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10001, 'Scott', 'Lawson','Computer Science', 11); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major, current_credits) 2 VALUES (10002, 'Mar', 'Wells','History', 4); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10003, 'Jone', 'Bliss','Computer Science', 8); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10004, 'Man', 'Kyte','Economics', 8); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10005, 'Pat', 'Poll','History', 4); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10006, 'Tim', 'Viper','History', 4); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10007, 'Barbara', 'Blues','Economics', 7); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10008, 'David', 'Large','Music', 4); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10009, 'Chris', 'Elegant','Nutrition', 8); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10010, 'Rose', 'Bond','Music', 7); 1 row created. SQL> SQL> INSERT INTO STUDENTS (id, first_name, last_name, major,current_credits) 2 VALUES (10011, 'Rita', 'Johnson','Nutrition', 8); 1 row created. SQL> SQL> INSERT INTO students (id, first_name, last_name, major,current_credits) 2 VALUES (10012, 'Sharon', 'Clear','Computer Science', 3); 1 row created. SQL> SQL> select * from major_stats; MAJOR TOTAL_CREDITS TOTAL_STUDENTS ------------------------------ ------------- -------------- Computer Science 22 3 Economics 15 2 Nutrition 16 2 History 12 3 Music 11 2 SQL> SQL> drop table students; Table dropped. SQL> drop table major_stats; Table dropped.