MySQL supports 4 TEXT field types (TINYTEXT, TEXT, MEDIUMTEXT and LONGTEXT) and this post looks at the maximum length of each of these field types.
MyISAM tables in MySQL have a maximum size of a row of 65,535 bytes, so all the data in a row must fit within that limit. However, the TEXT types are stored outside the table itself and only contribute 1 to 4 bytes towards that limit. (For more information about this refer to the MySQL Manual - Data Storage Requirements chapter).
TEXT data types are also able to store much more data than VARCHAR and CHAR text types so TEXT types are what you need to use when storing web page or similar content in a database.
The maximum amount of data that can be stored in each data type is as follows:
In most circumstances the TEXT type is probably sufficient, but if you are coding a content management system it's probably best to use the MEDIUMTEXT type for longer pages to ensure there are no issues with data size limits.
Оригинал статьи: http://www.electrictoolbox.com/maximum-length-mysql-text-field-types/