将SQL中的结果存储在数组中，以便在Php中传递JSON

This is my definition to handle result from MySQL. I need to put records from my request into data defined as array (data => array()). How do I put all my records from MySQL into my array?

$mydata = array('dataset_data' =>
(array('limit' => null,
 'transform' => null,
 'column_index' => null,
 'column_names' => array ('Name1','Name2', 'Name3', 'Name4', 'Name6', 'Name6', 'Age','Birthday'),
 'start_date' => '2006-08-28',
 'end_date' => '2018-08-24',
 'frequency' => 'daily',
 'data' => array()
)));