mysql - 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'

When I just pass the root the rowCount return correct result which is 0. However when I pass a node from lower rank(3rd), in the end of the recursive which is root, rowCount return 1?

PS

I use Mysql as DB

This is my table

main_id | sub_id
----------------    
    1   |    2    
    1   |    3    
    2   |    4    
    3   |    5

The code:

$stmt = $conn->prepare("Select * from table where sub_id= ? ");  

function get_path($stmt,$node,&$map){

    $res=$stmt->execute(array($node));

    if(!$res){ throw new Exception( implode(' ',$stmt->errorInfo()),1); }

        echo $node.' found '.$stmt->rowCount().'<br>';

        if($stmt->rowCount()==0){ //root
            $map[]=$node;
        }else{

            foreach($stmt->fetchAll(PDO::FETCH_ASSOC) AS $row){
                $map[]=$node;
                $upper_node=$row['main_id'];
                get_path($stmt,$upper_node,$map);
        }
    }

}

If I just pass get_path($stmt,1,$map); (the root)

the output:

1 found 0

but when I for example pass 4 into it the output become:

4 found 1
2 found 1
1 found 1 <= it should found 0

Why?

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.