exportCSV.php

<?php

function exportCSV(
    iterable $items,
    array $allowed_columns,
    ?string $sep = ';',
    ?string $filename = 'export.csv',
) {
    $output  = 'sep=' . $sep . PHP_EOL;
    
    foreach ($allowed_columns as $i => $allowed_column) {
        $output .= ($i > 0 ? $sep : '') . ucfirst($allowed_column);
    }
    
    $output .=  PHP_EOL;

    foreach ($items as $line) {
        $i = 0;

        foreach ($line as $column_name => $column_value) {
            if (in_array($column_name, $allowed_columns)) {
                $output .= ($i > 0 ? $sep : '') . $column_value;
                $i++;
            }
        }
        
        $output .=  PHP_EOL;
    }

    header('Content-type: application/csv');
    header('Content-Disposition: attachment; filename=' . $filename);

    print_r(mb_convert_encoding($output, "UTF-8", mb_detect_encoding($output)));
    //exit;
}

/**
 * ~~~~~~~~~~~~~~~~~~~~~~
 * Usage:
 * ~~~~~~~~~~~~~~~~~~~~~~
 */

$items = [
    0 => [ 'firstname' => 'Alice', 'lastname' => 'Henderson', 'email' => '[email protected]' ],
    1 => [ 'firstname' => 'John', 'lastname' => 'Doe', 'email' => '[email protected]' ],
    2 => [ 'firstname' => 'Bob', 'lastname' => 'Sanders', 'email' => '[email protected]' ],
];

// Or just:
// $items = $this->_dao->findItems(); // Query Database

exportCSV(
    $items,
    [ 'firstname'/*, 'lastname',*/ 'email' ],   // The 'lastname' column should be excluded
    // ';',                                     // The separator of your choice (Default: ';')
    // 'custom_export_name.csv',                // The filename of your choice (Default: 'custom_export_name.csv')
);