Mutating table problem help required

Question

Hi. I am rather hoping someone will be able to help me with this problem.
I have two tables, sa and mv. Create script below:
create table mv (
moduleId Char(2) CONSTRAINT ck_moduleId CHECK(moduleId in ('M1', 'M2', 'M3', 'M4', 'M5', 'M6', 'M7', 'M8')),
credits Number(2) CONSTRAINT ck_credits CHECK(credits in (10, 20, 40)),
constraint pk_mv primary key(moduleId)
create table sa (
stuId Char(2) CONSTRAINT ck_stuId CHECK(stuId in ('S1', 'S2', 'S3', 'S4', 'S5')),
moduleId Char(2),
constraint pk_sa primary key(stuId, moduleId),
constraint fk_moduleid foreign key(moduleId) references mv(moduleId)
And the scripts below is to insert data into both:
insert into mv VALUES('M1', 20)
insert into mv VALUES('M2', 20)
insert into mv VALUES('M3', 20)
insert into mv VALUES('M4', 20)
insert into mv VALUES('M5', 40)
insert into mv VALUES('M6', 10)
insert into mv VALUES('M7', 10)
insert into mv VALUES('M8', 20)
insert into sa VALUES('S1', 'M1')
insert into sa VALUES('S1', 'M2')
insert into sa VALUES('S1', 'M3')
insert into sa VALUES('S2', 'M2')
insert into sa VALUES('S2', 'M4')
insert into sa VALUES('S2', 'M5')
insert into sa VALUES('S3', 'M1')
insert into sa VALUES('S3', 'M6')
Now for the actual problems.
Firstly I need to try and overcome the mutating table problem by ensure that stuid = S1 in table sa can not take both moduleId M5 and M6.
Just one or the other. I have created a single trigger, but if fails because of the mutating table problem.
The second problem I need to overcome is that none of the stuids can have moduleIds where total credit value of more than 120 credits. Credit value is stored in the mv table.
Many thanks in advance for any assistance.

Answer 1

Use a statement level trigger:
Firstly I need to try and overcome the mutating table problem by ensure that stuid = S1 in table sa can not take both moduleId M5 and M6.
SQL> create or replace trigger sa_trg
  2  after insert or update on sa
  3  declare
  4  c number;
  5  begin
  6    select count(distinct moduleId) into c
  7    from sa
  8    where stuid = 'S1'
  9    and moduleId in ('M5','M6');
10    if c > 1 then
11       raise_application_error(-20001,'S1 on both M5 and M6!!');
12    end if;
13  end;
14  /
Trigger created.
SQL> select * from sa;
ST MO
S1 M1
S1 M2
S1 M3
S2 M2
S2 M4
S2 M5
S3 M1
S3 M6
8 rows selected.
SQL> insert into sa values ('S1','M5');
1 row created.
SQL> insert into sa values ('S1','M6');
insert into sa values ('S1','M6')
ERROR at line 1:
ORA-20001: S1 on both M5 and M6!!
ORA-06512: at "SCOTT.SA_TRG", line 9
ORA-04088: error during execution of trigger 'SCOTT.SA_TRG'
The second problem I need to overcome is that none of the stuids can have moduleIds where total credit value of more than 120 credits. Credit value is stored in the mv table
SQL> create or replace trigger sa_trg
  2  after insert or update on sa
  3  declare
  4  c number;
  5  begin
  6    select count(distinct moduleId) into c
  7    from sa
  8    where stuid = 'S1'
  9    and moduleId in ('M5','M6');
10    if c > 1 then
11       raise_application_error(-20001,'S1 on both M5 and M6!!');
12    end if;
13 
14    select count(*) into c from (
15    select stuid
16    from mv, sa
17    where sa.moduleid=mv.moduleid
18    group by stuid
19    having sum(credits)>120);
20 
21    if c > 0 then
22       raise_application_error(-20002,'A student cannot have more than 120 credits!!');
23    end if;
24 
25  end;
26  /
Trigger created.
SQL>   select stuid, sum(credits)
  2  from mv, sa
  3  where sa.moduleid=mv.moduleid
  4  group by stuid;
ST SUM(CREDITS)
S3           30
S2           80
S1          100
SQL> insert into sa
  2  values ('S1','M4');
1 row created.
SQL>   select stuid, sum(credits)
  2  from mv, sa
  3  where sa.moduleid=mv.moduleid
  4  group by stuid;
ST SUM(CREDITS)
S3           30
S2           80
S1          120
SQL> insert into sa
  2  values ('S1','M7');
insert into sa
ERROR at line 1:
ORA-20002: A student cannot have more than 120 credits!!
ORA-06512: at "SCOTT.SA_TRG", line 20
ORA-04088: error during execution of trigger 'SCOTT.SA_TRG'Max
http://oracleitalia.wordpress.com