I must store a flexible in to the database which could contain two values. Each one or zero.

What will be the littlest datatype to keep the information in MySQL?

A TINYINT(1) can contain amounts between -127 to 127.

You should use bit(1)

http://dev.mysql.com/doc/refman/5.0/en/storage-requirements.html

BOOL is saved in MySQL as TINYINT which may take 1 full byte

http://dev.mysql.com/doc/refman/5.0/en/other-vendor-data-types.html

A little(1) would normally also take 1-byte but when you will find multiple bits in one record, they get saved within the same byte, as much as 8 per byte.

Its a perfect situation for any boolean data type