Php PDO rowCount() return wrong result

Question

I have a function for getting path in a tree structure data.

According to my table in DB, root should get no result when I query sub_id=\'root_id\'

Answer 1

You shouldn't rely on PDOStatement::rowCount() to get the number of rows affected by a SELECT statement, see PHP manual, PDOStatement::rowCount:

DOStatement::rowCount() returns the number of rows affected by the last DELETE, INSERT, or UPDATE statement executed by the corresponding PDOStatement object.

If the last SQL statement executed by the associated PDOStatement was a SELECT statement, some databases may return the number of rows returned by that statement. However, this behaviour is not guaranteed for all databases and should not be relied on for portable applications.

[...]

Example #2 Counting rows returned by a SELECT statement

For most databases, PDOStatement::rowCount() does not return the number of rows affected by a SELECT statement. Instead, use PDO::query() to issue a SELECT COUNT(*) statement with the same predicates as your intended SELECT statement, then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned. Your application can then perform the correct action.

Answer 2

It is probably something to do with this from PDO rowCount Docs:

"If the last SQL statement executed by the associated PDOStatement was a SELECT statement, some databases may return the number of rows returned by that statement. However, this behaviour is not guaranteed for all databases and should not be relied on for portable applications."

In other words rowCount only really works with DML, and I believe this is the case in MySQL.

You have to count the fetched results to get the guaranteed row count.

Answer 3

Eg of @VMai 's Correct Answer:

$query = $db->prepare("

  SELECT COUNT(*) FROM table
  WHERE
       whatever
 ");

$query->execute();

$result = $query->fetchColumn();

if ($result > 5)
{
echo "Result is greater than 5";
}
else
{
echo "Result is less than 5";
}
?>

Note: You will need to run the "real" SQL Query again, except without COUNT(*).