Empty IN clause parameter list in MySQL

Question

What happens when you do a SQL query where the IN clause is empty?

For example:

SELECT user WHERE id IN ();

Will MySQL

Answer 1

If you use AUTO_INCREMENT for id (1,2,3, ..) and if array is empty, you can add one item [0]. So it will be

if (empty($arr)) {
   $arr[] = 0;
}

SELECT user WHERE id IN (0);

And there will be no mysql parse error. This case is very usefull in subqueries - when your main query is not dependent on subquery results.

---

Better way - don't call the query if array is empty.

$data = null;
if (!empty($arr)) {
    $data = ... call query
}