prevent sql injection on query with variable (and large) number of columns - php

Question

I have a sql query that is generated using php. It returns the surrogate key of any record that has fields matching the search term as well as any record that has related records in other tables matching the search term.
I join the tables into one then use a separate function to retrieve a list of the columns contained in the tables (I want to allow additions to tables without re-writing php code to lower ongoing maintenance).
Then use this code
foreach ($col_array as $cur_col) {
foreach ($search_terms_array as $term_searching) {
$qry_string.="UPPER(";
$qry_string.=$cur_col;
$qry_string.=") like '%";
$qry_string.=strtoupper($term_searching);
$qry_string.="%' or ";
}
}
To generate the rest of the query string
select tbl_sub_model.sub_model_sk from tbl_sub_model inner join [about 10 other tables]
where [much code removed] or UPPER(tbl_model.image_id) like '%HONDA%' or
UPPER(tbl_model.image_id) like '%ACCORD%' or UPPER(tbl_badge.sub_model_sk) like '%HONDA%'
or UPPER(tbl_badge.sub_model_sk) like '%ACCORD%' or UPPER(tbl_badge.badge) like '%HONDA%'
or UPPER(tbl_badge.badge) like '%ACCORD%' group by tbl_sub_model.sub_model_sk
It does what I want it to do however it is vulnerable to sql injection. I have been replacing my mysql_* code with pdo to prevent that but how I'm going to secure this one is beyond me.
So my question is, how do I search all these tables in a secure fashion?

Answer 1

Here is a solution that asks the database to uppercase the search terms and also to adorn them with '%' wildcards:
$parameters = array();
$conditions = array();
foreach ($col_array as $cur_col) {
foreach ($search_terms_array as $term_searching) {
$conditions[] = "UPPER( $cur_col ) LIKE CONCAT('%', UPPER(?), '%')";
$parameters[] = $term_searching;
}
}
$STH = $DBH->prepare('SELECT fields FROM tbl WHERE ' . implode(' OR ', $conditions));
$STH->execute($parameters);
Notes:
We let MySQL call UPPER() on the user's search term, rather than having PHP call strtoupper()
That should limit possible hilarious/confounding mismatched character set issues. All your normalization happens in one place, and as close as possible to the moment of use.
CONCAT() is MySQL-specific
However, as you tagged the question [mysql], that's probably not an issue.
This query, like your original query, will defy indexing.

Answer 2

Try something like this using an array to hold parameters. Notice % is added before and after term as LIKE %?% does not work in query string.PHP Manual
//Create array to hold $term_searching
$data = array();
foreach ($col_array as $cur_col) {
foreach ($search_terms_array as $term_searching) {
$item = "%".strtoupper($term_searching)."%";//LIKE %?% does not work
array_push($data,$item)
$qry_string.="UPPER(";
$qry_string.=$cur_col;
$qry_string.=") LIKE ? OR";
}
}
$qry_string = substr($qry_string, 0, -3);//Added to remove last OR
$STH = $DBH->prepare("SELECT fields FROM table WHERE ". $qry_string);//prepare added
$STH->execute($data);
EDIT
$qry_string = substr($qry_string, 0, -3) added to remove last occurrence of OR and prepare added to $STH = $DBH->prepare("SElECT fields FROM table WHERE". $qry_string)