MySQL 3种text类型的最大长度如下：
- TEXT 65,535 bytes ~64kb
- MEDIUMTEXT 16,777,215 bytes ~16Mb
- LONGTEXT 4,294,967,295 bytes ~4Gb
参考
http://www.cnblogs.com/jirglt/p/3558782.html
http://blog.sina.com.cn/s/blog_4f925fc30102edg8.html
http://justdo2008.iteye.com/blog/576552
