1、把插件放到这个目录下：
mysqlserver to use sha256 algorithm. I downloaded source from http://stuge.se/mysql-sha256/mysql-sha256-3.tar.bz2, compiled and put in /usr/local/lib/mysql/plugin/
2、创建函数SHA256
create function sha256 returns string soname ‘sha256.so’;
select sha256(‘aaaa’);