why {if row exist then fetch them} does not work? - php

Question

I want to check {if row exist} first and then fetch the results. here is my code:
$id = 102;
// connecting to database here
$sth = $dbh->prepare('SELECT * FROM users WHERE id = ?');
$sth->execute(array($id));
$num_rows = $sth->fetchColumn();
// if exist
if($num_rows){
// then fetch
while($end = $sth->fetch())
{
echo $end['id'];
}
}
But the output is blank, Why ?
It should be noted that the row with id = 102 is exist in the database.

Answer 1

As I understood, you have only one row with this ID. You can use fetch():
$id = 102;
// connecting to database here
$sth = $dbh->prepare('SELECT * FROM users WHERE id = ?');
$sth->execute(array($id));
$row = $sth->fetch();
// if record exist
if ($row) {
var_dump($row);
die();
}

Answer 2

PDO also have similar method rowCount but that would return effected rows in some cases.
Quoting from PHP Manual
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.
As suggested, you can query, count and proceed
$id = 102;
// connecting to database here
$sth = $dbh->prepare('SELECT COUNT(*) FROM users WHERE id = ?');
$sth->execute(array($id));
$num_rows = $sth->fetchColumn();
// if exist
if($num_rows > 0){
$sth = $dbh->prepare('SELECT * FROM users WHERE id = ?');
$sth->execute(array($id));
// then fetch
while($end = $sth->fetch())
{
echo $end['id'];
}
}