Why '(' change to ( ?

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Dear my friends,

I meet a problem.

$query = $this->db->query("SELECT p_endgrid_i('".$date."','".$cb_line."','".$cb_model."','".$cb_process."','".$url_item."');");

The data of $url_item has '()',i don't know why they are changed to '& #40;& #41;' in process of MySQL.
I try many times,i found it isn't CI function and mysql problem.
And echo $url_item is nomarl in html page.
Now i don't know how to solution this problem,and i want to know why it happen?

Plz help!
Thank you very much!

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2014/12/02

I found it maybe is recognized as a character or array.
Now,I use the following way to solution my problem.
$url_temp3 = str_replace("& #40;","(",$url_temp2);
$url_item = str_replace("& #41;",")",$url_temp3);

I want to know another right way, i think it is a temporary method.
And i want to know why so much!

Thank you my friends!