错误：创建功能sys_exec返回int SONAME'lib_mysqludf_sys.so';

Question

我正在使用phpMyAdmin，并且想从MySQL触发器调用PHP脚本，所以我按照此Invoking a PHP script from a MySQL trigger的步骤进行操作，但是当我在phpMyAdmin中查询以下代码时：

DROP FUNCTION IF EXISTS sys_eval;
CREATE FUNCTION sys_eval RETURNS string SONAME 'lib_mysqludf_sys.so';

有错误：

Error

Static analysis:

1 errors were found during analysis.

    A "RETURNS" keyword was expected. (near "RETURNS" at position 25)

SQL query:

CREATE FUNCTION sys_exec RETURNS int SONAME 'lib_mysqludf_sys.so'

MySQL said: Documentation
#1126 - Can't open shared library 'lib_mysqludf_sys.so' (errno: 2, The specified module could not be found.
)

我该如何解决？