LONGTEXT [CHARACTER SET charset_name] [COLLATE collation_name]

A TEXT column with a maximum length of 4,294,967,295 or 4GB (232 - 1)
characters. The maximum effective (permitted) length of LONGTEXT
columns depends on the configured maximum packet size in the
client/server protocol and available memory.

URL: http://dev.mysql.com/doc/refman/5.0/en/string-type-overview.html

