How to get data from table, making date as key and corresponding data?

Question

  id sender_id receiver_id msg  date_added
    1    2          5       hii     2018-10-24 16:42:41
    2    5          2       hello     2018-10-25 16:42:41

i want to extract data as:

[2018-10-24]=>[{
                sender_id=>2,
                receiver_id=>5,
                msg=>hii}],
[2018-10-25]=>[{
               sender_id=>5,
                receiver_id=>2,
                msg=>hello
              }]

I have done this by first querying for the date first and applying group by to dates. then looping through dates and finding the data for those dates. but i think use of loops for that much of dates and that much of user will make the app slow in the coming future

The code i have used is as:

//the dates is used to get the dates from table using group by
$dates = $this->get_date_list($checkArr);
////then i loop through each date to get the corresponding data
foreach($dates as $key=>$value){
    $msg = $this->get_msg_by_date($value,$checkArr);
    $data[$value] = $msg;
}

//here is the code to get the date from the date column
public function get_date_list($checkArr){
    $sql = "Select date(date_added) as new_date from tb_chats where (sender_id = $checkArr[sender_id] AND receiver_id = $checkArr[receiver_id]) OR (sender_id = $checkArr[receiver_id] AND receiver_id = $checkArr[sender_id]) GROUP BY new_date";
    $query = $this->db->query($sql);
    $data  = $query->result_array();
    return array_column($data,'new_date');
}

//here is the code to get the data for the looped dates
public function get_msg_by_date($date,$checkArr){
    $sql = "Select * from tb_chats where (sender_id = $checkArr[sender_id] AND receiver_id = $checkArr[receiver_id] AND date_added LIKE '$date%') OR (sender_id = $checkArr[receiver_id] AND receiver_id = $checkArr[sender_id] AND date_added LIKE '$date%')";
    $query = $this->db->query($sql);
    $data  = $query->result_array();
    return $data;
}

Answer 1

get date field as a comma separated string along with the query( CONCAT ). Use array_combine method. First parameter will be the output of explode(',', CONCAT STRING) and the second parameter is the result array. The output is what you are looking for.