Which MySQL data type to use for storing boolean values

Question

Since MySQL doesn\'t seem to have any \'boolean\' data type, which data type do you \'abuse\' for storing true/false information in MySQL?

Especially in the context

Answer 1

This is an elegant solution that I quite appreciate because it uses zero data bytes:

some_flag CHAR(0) DEFAULT NULL

To set it to true, set some_flag = '' and to set it to false, set some_flag = NULL.

Then to test for true, check if some_flag IS NOT NULL, and to test for false, check if some_flag IS NULL.

(This method is described in "High Performance MySQL: Optimization, Backups, Replication, and More" by Jon Warren Lentz, Baron Schwartz and Arjen Lentz.)