How to Reset the Array Pointer in PDO Results for Multiple Iterations?

PDO Resetting Array Pointer in Results

In the transition from MySQL to PDO methods, one may encounter challenges when attempting to iterate through a fetched array twice, commencing from row zero each time. The solution lies in understanding the differences in approach between the two methods.

Under the MySQL framework, the mysql_data_seek function rewinds the row pointer to a specific position within the resultant array. In PDO, however, this functionality is not directly available. Instead, one can employ two alternative techniques to achieve the desired outcome.

Saving Results to an Array

The first approach involves storing the results in an array, as demonstrated in the code snippet below:

$pdo = new PDO('mysql:host=' . $host . ';dbname='.$database, $username, $password);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$stmt = $pdo->prepare('SELECT * FROM mytable WHERE active = 1 ORDER BY name ASC');
$stmt->setFetchMode(PDO::FETCH_ASSOC);
$stmt->execute();

$rows = $stmt->fetchAll();

foreach ($rows as $r) {
    // first run
}

foreach ($rows as $r) {
    // second run
}

By utilizing the fetchAll method, the entire result set is stored in the $rows array, allowing for multiple iterations with the reset pointer.

Re-Execution of Query

Alternatively, one can opt to re-execute the query. While less efficient than the array storage method, this approach may suffice when the result set is relatively small.

$pdo = new PDO('mysql:host=' . $host . ';dbname='.$database, $username, $password);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$stmt = $pdo->prepare('SELECT * FROM mytable WHERE active = 1 ORDER BY name ASC');
$stmt->setFetchMode(PDO::FETCH_ASSOC);

while($row = $stmt->fetch())
{
    // first run
}

$stmt->execute(); //re-execute the query

while($row = $stmt->fetch())
{
    // second run
}

By re-executing the query, a new result set is generated, with the pointer starting at row zero. This approach ensures that both iterations have access to the full data set.

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