MySQL. Working with Integer Data Interval

I've just started using SQL, so that have no idea how t work with not standard data types. I'm working with MySQL... Say, there are 2 tables: Stats and Common. The Common table looks like this:

CREATE TABLE Common (
    Mutation VARC开发者_运维技巧HAR(10) NOT NULL,
    Deletion VARCHAR(10) NOT NULL, 
    Stats_id ??????????????????????,
    UNIQUE(Mutation, Deletion) );

Instead of ? symbols there must be some type that references on the Stats table (Stats.id). The problem is, this type must make it possible to save data in such a format: 1..30 (interval between 1 and 30). According to this type, it was my idea to shorten the Common table's length.

Is it possible to do this, are there any different ideas?

Assuming that Stats.id is an INTEGER (if not, change the below items as appropriate):

first_stats_id INTEGER NOT NULL REFERENCES Stats(id)
last_stats_id  INTEGER NOT NULL REFERENCES Stats(id)

Given that your table contains two VARCHAR fields and an unique index over them, having an additional integer field is the least of your concerns as far as memory usage goes (seriously, one integer field represents a mere 1GB of memory for 262 million lines).