How to use trigger to catch the sum of a column is greater than 1

Question

Here is my problem.
I create a table, which is preference( name char, percentage real);
the sum of the percentage for some user(name) should be 1;
And one user can have many records in the table as needed.
I should to validate the insert data which is valid after a series of insert operation? How can I do it?

Answer 1

Exactly what I was thinking:
SQL> create table preference
  2  (
  3  name varchar2(20),
  4  percentage number(3)
  5  );
Table created
SQL> create materialized view preference_mv
  2  refresh on commit
  3  as select name,sum(percentage) total_percentage
  4  from preference
  5  group by name;
Materialized view created
SQL> alter table preference_mv add constraint c_pref_pct check (total_percentage = 100);
Table altered
SQL> insert into preference values ('name1',25);
1 row inserted
SQL> insert into preference values ('name1',50);
1 row inserted
SQL> insert into preference values ('name1',25);
1 row inserted
SQL> commit;
Commit complete
SQL> insert into preference values ('name2',10);
1 row inserted
SQL> insert into preference values ('name2',30);
1 row inserted
SQL> commit;
commit
ORA-12008: error in materialized view refresh path
ORA-02290: check constraint (SCOTT.C_PREF_PCT) violatedSQL>