How to use a quoted string variable in a MySqli prepared statement? - php

Question

Sorry if this seems a really stupid question, but I'm struggling to get to grips with changing from Mysql to Mysqli and prepared statements.
So in mysql, I would have done this:
$q=('SELECT * FROM table WHERE field="'.$variable.'"');
$result = mysql_query($q);
I now know this is not good. So I now have the below:
$stmt = $mysqli->prepare('SELECT * FROM table WHERE field=? LIMIT 1');
$stmt->bind_param('s', $variable);
$stmt->execute();
Problem is that the query doesn't work. Say the ? is actually "tree". So the query becomes:
'SELECT * FROM table WHERE field=tree LIMIT 1'
If I tried to run that query in say phpmyadmin I get "Unknown column tree in where clause". Obviously if I put quotes around it then it works, hence the original query. So how can I get this to work if I can't use quotes, since then you are looking for the literal question mark?
For reference I am then using this code:
$meta = $stmt->result_metadata();
while ($field = $meta->fetch_field()) {
$parameters[] = &$row[$field->name];
}
call_user_func_array(array($stmt, 'bind_result'), $parameters);
while ($stmt->fetch()) {
foreach($row as $key => $val) {
$x[$key] = $val;
}
$results[] = $x;
}
As I can't use get_result() which is very annoying. I have PHP version 5.4, and even the mysqlnd driver, but can't enable it as I'm on a VPS and my host says it might affect other sites on that server. Consequently what is actually just two lines in MySql is actually now something like 15 lines in the 'improved' mysqli. Great.
Any help would be appreciated!

Answer 1

This:
$stmt = $mysqli->prepare('SELECT * FROM table WHERE field=? LIMIT 1');
$stmt->bind_param('s', $variable);
is not equivalent to this:
SELECT * FROM table WHERE field=tree LIMIT 1
Prepared statement placeholders are not the same as copy and pasting in values. You are binding the value "tree" as a string here, the database will actually understand this. The ? is not simply being replaced by the bound value, the database understands the difference between your query structure with its placeholders and the values you're binding into them. Binding the parameter this way is equivalent to running:
SELECT * FROM table WHERE field='tree' LIMIT 1

Answer 2

Consequently what is actually just two lines in MySql is actually now something like 15 lines in the 'improved' mysqli. Great.
Mysqli is not intended to be used as is. It is but a building material for the higher level library. When used wisely, it can give you data in one line:
$data = $db->getAll('SELECT * FROM table WHERE field=?s', $variable);
(BTW, the same goes for the old mysql ext as well)