Php正则表达式查找字符串是否为mysql选择语句

我在执行查询之前试图验证查询，如果查询不是mysql选择语句，那么我必须向用户显示消息。

我发现下面的regex从这个链接:使用正则表达式

$reg="/^Select's+(?:'w+'s*(?:(?=from'b)|,'s*))+from's+'w+'s+where's+'w+'s*='s*'[^']*'$/i"; 

接下来我写了下面的代码，但是它总是打印not select query ($match每次都是空的)

$string="select * from users where id=1";
preg_match_all($reg,$string,$match);
if(!empty($match)){
echo "select query";
//execute and process result
//$this->user_model->list($string);
}else{
   echo "not select query";
   //show_message('inv_query');
}

请纠正正则表达式以验证sql select语句(select, from,where, join, orderderby groupby都可以在select语句中出现)。或者让我知道其他更好的方法来完成这项任务。

/*
some sample select statements
select * from users where id=1;
select * from users where id=1 AND name= 'Prabhu';
select * from users where id=1 AND name= 'Prabhu' order by name;
Select * from users where id=1 AND name= 'Prabhu' group by id order by name;
Select * from users join role on users.role_id=role.id where id=1 AND name= 'Prabhu' group by id order by name;
*/