Why won't CodeIgniter return the result from a SQL query when parentheses are in it?

Question

When I have a SQL query built that contains parentheses in one of the search values, I do not get the result that I am expecting. However, if I run the query on my database directly I have the expected result returned.

Also, if my search does not contain parentheses it will properly return the expected result.

CodeIgniter model function:

function get_submodels($params)
{
 $sql = "SELECT DISTINCT(`a`.`submodel`), `a`.`model_id` FROM `models` AS `a`"
 . "LEFT JOIN `manufacturers` AS `b` ON `a`.`manufacturer` = `b`.`manufacturer_id`"
 . "WHERE `a`.`year` = ? AND `b`.`manufacturer` = ? AND `a`.`model` = ?"
 . "ORDER BY `a`.`submodel` ASC;";

 $query = $this->db->query($sql, $params);

 return $query->result();
}

An example of a working query:

"... WHERE `a`.`year` = '2007' AND `b`.`manufacturer` = 'CHEVROLET' AND `a`.`model` = 'MONTE CARLO'"

An example of a non-working query:

"... WHERE `a`.`year` = '2007' AND `b`.`manufacturer` = 'MERCEDES BENZ' AND `a`.`model` = 'CLK350 (W209)'"

I have used $this->db->last_query() and the query is formatted properly. Even copying the last query that has no results and running it against the database directly will get the result expected.

Answer 1

Despite running $this->db->last_query() and seeing the query as being proper, I decided to enable profiling on the page. My results show that the parenthesis where being encoded into HTML entities.

Therefore, the query was being formed as this:

"... WHERE `a`.`year` = '2007' AND `b`.`manufacturer` = 'MERCEDES BENZ' AND `a`.`model` = 'CLK350 (W209)'"

Instead of this:

"... WHERE `a`.`year` = '2007' AND `b`.`manufacturer` = 'MERCEDES BENZ' AND `a`.`model` = 'CLK350 (W209)'"

I resolved this by modifying the insert query to use htmlentities for these columns and updated all existing records. While I knew the Codeigniter would escape values I was not aware that it would encode them as well.