What I´m trying is to create a column on the table that only accepts 3 values.
I know in Access you can add a validation rule for it, but I´m wondering what is the rigth syntax for PL/SQL.
I believe another way around would be to create a second table and create a foreign key, but seem to be too much hassle for something so silly.
If it is a very small list of values and the list will not change, then you might want a CHECK constraint. For example, CREATE TABLE TEST (col1 varchar2(50) CONSTRAINT putnamehere CHECK (col1 IN ('PAID','APPROVAL')) ENABLE VALIDATE);
The above can also be done with a trigger, but triggers are much slower than column level constraints.
If the list of values is large, or the values might change over time, then it is best to use another table and a foreign key constraint.