Mega Code Archive
Avoid the mutating table error
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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> 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> CREATE OR REPLACE PACKAGE StudentData AS
2 TYPE t_Majors IS TABLE OF lecturer.major%TYPE
3 INDEX BY BINARY_INTEGER;
4 TYPE t_IDs IS TABLE OF lecturer.ID%TYPE
5 INDEX BY BINARY_INTEGER;
6
7 myLecturerMajors t_Majors;
8 myLecturerIDs t_IDs;
9 v_NumEntries BINARY_INTEGER := 0;
10 END StudentData;
11 /
Package created.
SQL>
SQL> CREATE OR REPLACE TRIGGER RLimitMajors
2 BEFORE INSERT OR UPDATE OF major ON lecturer
3 FOR EACH ROW
4 BEGIN
5 StudentData.v_NumEntries := StudentData.v_NumEntries + 1;
6 StudentData.myLecturerMajors(StudentData.v_NumEntries) :=
7 :new.major;
8 StudentData.myLecturerIDs(StudentData.v_NumEntries) := :new.id;
9 END RLimitMajors;
10 /
Trigger created.
SQL>
SQL> CREATE OR REPLACE TRIGGER SLimitMajors
2 AFTER INSERT OR UPDATE OF major ON lecturer
3 DECLARE
4 studentMax CONSTANT NUMBER := 5;
5 studentCount NUMBER;
6 myLecturerID lecturer.ID%TYPE;
7 v_Major lecturer.major%TYPE;
8 BEGIN
9 FOR v_LoopIndex IN 1..StudentData.v_NumEntries LOOP
10 myLecturerID := StudentData.myLecturerIDs(v_LoopIndex);
11 v_Major := StudentData.myLecturerMajors(v_LoopIndex);
12
13 SELECT COUNT(*)
14 INTO studentCount
15 FROM lecturer
16 WHERE major = v_Major;
17
18 IF studentCount > studentMax THEN
19 RAISE_APPLICATION_ERROR(-20000,
20 'Too many lecturer for major ' || v_Major ||
21 ' because of student ' || myLecturerID);
22 END IF;
23 END LOOP;
24
25 StudentData.v_NumEntries := 0;
26 END SLimitMajors;
27 /
Trigger created.
SQL>
SQL> UPDATE lecturer
2 SET major = 'History'
3 WHERE ID = 10003;
1 row updated.
SQL>
SQL> UPDATE lecturer
2 SET major = 'History'
3 WHERE ID = 10002;
1 row updated.
SQL>
SQL> UPDATE lecturer
2 SET major = 'History'
3 WHERE ID = 10009;
1 row updated.
SQL>
SQL>
SQL> drop table lecturer;
Table dropped.
SQL>
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