MySql column value to indicate 2 possible options
You can use the MySQL ENUM type which is stored as a one-byte int internally. From the docs which only hint on implementation,


  Inserting 1 million rows into this table with a value of 'medium' would require 1 million bytes of storage, as opposed to 6 million bytes if you stored the actual string 'medium' in a VARCHAR column.


Though it's documented elsewhere explicitly,


  1 or 2 bytes, depending on the number of enumeration values (65,535 values maximum)


MySQL can use two byte enums if you have 255&lt;x&lt;65,535 potential values to enumerate over.

It looks like this,

CREATE TABLE payment (
    id      int  AUTO_INCREMENT,
    payment ENUM('money', 'online'),
    PRIMARY KEY (id)
);