MySQL: left JOIN vs. LEFT JOIN

Question

I have the following sql query

SELECT * FROM jos_jcalpro_events AS e 
  LEFT JOIN jos_jcalpro_events_seats AS s ON e.extid = s.extid
  LEFT JOIN jos_jcalpro_events_types_xref AS t ON e.extid = t.extid

which I execute via PDO from PHP. I create out of this another query to reinsert in the database. But it doesn't work. When I change LEFT from upper to lower case it does:

SELECT * FROM jos_jcalpro_events AS e 
  left JOIN jos_jcalpro_events_seats AS s ON e.extid = s.extid
  left JOIN jos_jcalpro_events_types_xref AS t ON e.extid = t.extid

In my creating routine there is no difference but the created INSERT has actually 2 lines less. How can that be?

Here is the important part of the code:

    $resource = JcalproDataImport::getInstance();

    // IMPORT
    $pdo = $resource->getConnection('import', 'pdo');
    $events = $pdo->query(
        'SELECT * FROM jos_jcalpro_events AS e '
        .'left JOIN jos_jcalpro_events_seats AS s ON e.extid = s.extid '
        .'left JOIN jos_jcalpro_events_types_xref AS t ON e.extid = t.extid;')->fetchAll(PDO::FETCH_ASSOC);

    // MAPPING
    $map = array(
        'picture'=>null, 'cat'=>null, 'day'=>null, 'month'=>null, 'year'=>null, 'recur_type'=>null, 'checked_out'=>null,
      'checked_out_time'=>null, 'payment_type'=>null, 'id'=>null,
      'extid'=>'id', 'contact'=>'contact_info', 'start_date'=>'start', 'end_date'=>'end', 'recur_val'=>'repeat_period',
      'recur_end_type'=>'repeat_end_type_id', 'recur_count'=>'repeat_end_after_occurrences',
      'recur_until'=>'repeat_end_after_date', 'wp_only'=>'only_in_wp', 'eticket'=>'prevent_sending_eticket',
      'region'=>'region_id', 'onlinebooking'=>'online_booking_form', 'organiser'=>'organiser_name'
    );

    // OUTPUT
    $pdo = $resource->switchConnection('export', 'pdo');
    $pdo->query('SET foreign_key_checks = 0');

    foreach ($events as $values)
    {
        $values['chargeable_status'] = (strtolower($values['payment_type']) == 'p') ? 1 : 0;
        $values['repeat_period_type_id'] = $repeat_period_type_map[$values['recur_type']];
        foreach($map as $from=>$to)
        {
            if ($to!== null){ $values[$to] = $values[$from]; }
            unset( $values[$from] );
        }
        $values['created_at'] = '2008-01-01';
        $values['updated_at'] = $values['created_at'];

          if (!$event) {
              foreach ($values as $field=>$value)
              {
                  $sql .= ', '.$field;
                  $sqlValues .= ', "'.mysql_real_escape_string($value).'"';
              }
              $sql = 'INSERT INTO event ( '.substr($sql, 2).' ) VALUES '.PHP_EOL.'( '.substr($sqlValues, 2).' )';
          }else{
              foreach ($values as $value)
              {
                  $sqlValues .= ', "'.mysql_real_escape_string($value).'"';
              }
              $sql .= ', ( '.substr($sqlValues, 2).' )';
          }
        $event[] = $values;
    }
    $pdo->query($sql)

But it works fine for other queries, so that I can't believe in a problem there.

Answer 1

1. There is no reason left JOIN would work differently than LEFT JOIN. That's very unlikely to be related to your problem.

2. Do your column name mapping with column aliases in your SELECT.

3. Omit columns you don't want by naming those columns you do want, instead of using SELECT *.

4. Prepare the INSERT once, with named parameters matching the column alias names. Then use execute($values) to insert each row fetched from the SELECT.

Here's approximately how I'd write it:

$map = array(
  'extid'=>'id', 
  'contact'=>'contact_info', 
  'start_date'=>'start', 
  'end_date'=>'end',
  'recur_val'=>'repeat_period', 
  'recur_end_type'=>'repeat_end_type_id', 
  'recur_count'=>'repeat_end_after_occurrences',
  'recur_until'=>'repeat_end_after_date',
  'wp_only'=>'only_in_wp',
  'eticket'=>'prevent_sending_eticket',
  'region'=>'region_id',
  'onlinebooking'=>'online_booking_form',
  'organiser'=>'organiser_name',
  'CURDATE()'=>'created_at',
  'CURDATE()'=>'updated_at',
);

$aliasize = function($alias, $column) { return "$column AS $alias"; }
$select_list = join(",", array_walk($aliasize, $map));

$events = $pdo->query("SELECT $select_list FROM ...")
    ->fetchAll(PDO::FETCH_ASSOC);

$column_list = join(",", array_values($map));
$parameterize = function($alias) { return ":$alias"; }
$param_list = join(",", array_map($parameterize, $map));

$insert = $pdo->prepare("INSERT INTO event ($column_list) VALUES ($param_list)");

foreach ($events as $values) {
    $insert->execute($values);
}