fields('t')

$myId = 5;

$result = db_select('table', 't')

->fields('t')

->condition('id', $myId, '=')

->execute()

->fetchAssoc();

?>

the above is equivelent to:

SELECT t.* FROM table as t WHERE t.id = 7

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http://stackoverflow.com/questions/19683409/drupal-query-builder-return-all-fields