This is an example of a DML trigger. : After Delete Trigger « Trigger « Oracle PL / SQL






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.

 








Related examples in the same category

1.Create an after delete trigger