PHP different results for mysql_query and pdo - php

Question

I am trying to convert a mysql_query to pdo equivalent
My table structure is (removed unrelated columns - the one needed for my question is other_id) :
CREATE TABLE `temp_table` (
`id` int(12) NOT NULL DEFAULT '0',
`other_id` int(12) NOT NULL DEFAULT '0',
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
And the data it has:
-----------------
| id | other_id |
-----------------
| 1 | 123 |
-----------------
| 2 | 0 |
-----------------
| 3 | 456 |
-----------------
| 4 | 0 |
-----------------
The previous database query was :
$sql = "SELECT id FROM temp_table WHERE other_id = '{$other_id}'";
$result = mysql_query($sql, $db)
return mysql_fetch_assoc($result);
The query is called with $other_id as NULL ("null" in php and not string or anything).
Result mysql_query : This gives my values 2,4
PDO equivalent code :
$sql = "SELECT id FROM temp_table WHERE other_id = :other_id";
$sth = $dbConnection->prepare($sql);
$sth->bindValue(":other_id", $other_id);
$sth->execute();
return $sth->fetchAll(PDO::FETCH_COLUMN);
Result PDO : This gives no values at all.
This is weird issue which I have not encountered before (since I am more java developer and recently touched PHP after few years).
As a workaround I had to put below line to return 2,4 as result from pdo output, but want to understand more about the difference mentioned above.
$sth->bindValue(":other_id", empty($other_id) ? 0 : $other_id);
I also tried $sth->bindValue(":other_id", $other_id, PDO::PARAM_INT); which did not help

Answer 1

This is not an issue with the mysql_ vs PDO difference, but rather with type-juggling.
In the first non-PDO example, $other_id is being converted to a string in the query, so your query looks like this:
SELECT id FROM temp_table WHERE other_id = '';
MySQL treats an empty string the same as 0 for fields of numeric type during queries, so your query is actually correctly matching two records.
In the PDO example since you're passing $other_id (which is null), your query is bound as follows:
SELECT id FROM temp_table WHERE other_id = NULL;
MySQL does not treat 0 as NULL, so the queries that you're sending are actually not the same.

Answer 2

This is weird issue which I have not encountered before.
There is nothing weird here.
When $other_id is NULL the first query becomes:
SELECT id FROM temp_table WHERE other_id = ''
Because the type of the other_id column is numeric, the provided value (the empty string) is converted to the number 0 and there are two matching rows.
On the other hand, the query sent through PDO is equivalent to:
SELECT id FROM temp_table WHERE other_id = NULL
Not only that there are no NULLs in the table, but this query never returns any row, even if there are rows having NULL in the column other_id. (The correct way to select the rows having NULL in other_id is to use the IS NULL operator).