How to create row in a table with the sum of 1 sql

Question

I am trying to create table with division possibilities and i want that the sum of all the cells in one row will be 1. For example:

0.1, 0.2, 0.3, 0.3, 0.1  

Answer 1

You can create a constraint on the table that requires each row to meet some condition, in this case that total of columns be 1:

create table my_table (
  col1 number,
  col2 number,
  col3 number,
  col4 number,
  constraint assert_sum_is_one check (col1 + col2 + col3 + col4 = 1)
)

Any attempt to insert or update rows to not total 1 will cause a constraint violation exception.

Answer 2

If you are on 11g you can use an Oracle Virtual Column:

http://www.oracle-base.com/articles/11g/virtual-columns-11gr1.php

in conjunction with a check constraint.

CREATE TABLE myTable (
  id          NUMBER,
  col1        NUMBER(3),
  col1        NUMBER(3),
  col3        NUMBER(3),
  colsum      NUMBER GENERATED ALWAYS AS (col1 + col2 + col3) VIRTUAL,
  CONSTRAINT pk_mytable PRIMARY KEY (id)
);

and then add a constraint to check that colsum is always exactly 1.

EDIT: Bohemian's answer is simpler and better. The only advantage in this case with a virtual column is that the sum is always persisted/visible, but if a constraint prevents the sum from being anything other than 1, then that isn't necessary. I'll leave this answer in just for the sake of the completion.