PHP / MySQL n-ая строка с DATE_SUB и т. Д.

Итак, у меня есть таблица, я использую для графика некоторых данных. id, agcid, ooscount, date

Данные - это образцы каждые 5 минут, для 18 объектов ID - автоматическое приращение, agcid - идентификатор объекта, дата - самообучение, а ooscount - целочисленный столбец.

В настоящее время я использую это:

$sql2 = "SELECT ooscount, date 
          FROM ooscount 
          where agcid = '".$agcid."' AND date >= DATE_SUB(NOW( ),INTERVAL 7 HOUR) 
          order by date  DESC";

Простой, но эффективный, однако у меня есть чрезвычайно большой набор данных, который усложняет графики.

Я попытался добавить AND ooscount.id mod 3 = 0 к этому, однако наборы данных для каждого agcid казались очень случайными, у некоторых была только пара, у других - в 5 раз больше, чем следовало бы.

Затем я попробовал такой подход:

  $sql2 = "set @row:=-1; 
        SELECT ooscount.*
        FROM
            ooscount
            INNER JOIN
            (
                SELECT id
                FROM
                    (
                        SELECT @row:=@row+1 AS rownum, id 
                        FROM
                            (
                                SELECT id, date, ooscount FROM ooscount where agcid = '".$agcid."' and date >= DATE_SUB(NOW( ),INTERVAL 12 HOUR) order by date DESC
                            ) AS sorted
                    ) as ranked
                WHERE rownum % 3 = 0
            ) AS subset
                ON subset.id = ooscount.id;";

Он прокомментировал, простите //. Однако этот подход, когда он работает в phpMyAdmin, дает мне следующее:

PHP Fatal error:  Call to a member function fetch_assoc()
on a non-object in /var/www/khamlin/oosagc.php on line 145

Наконец, часть кода для отображения этого:

$result2 = $conn->query($sql2);
$rowsarray = "";
//var_dump($result2);
while ($row2 = $result2->fetch_assoc()) {

Я считаю, что проблема заключается в том, что примеры, которые я нашел, не ожидают множества наборов данных в одной таблице, и, следовательно, ID будет инкрементным (то есть: 1,2,3,4,5,6 и т.д.), А не ( 168006, 168023, 168041, 168060).

Как я могу изменить это, чтобы удовлетворить мои потребности?

Состав

CREATE TABLE IF NOT EXISTS 'ooscount' ( 'id' int(10) NOT NULL AUTO_INCREMENT, 'agcid' int(3) NOT NULL, 'ooscount' int(10) NOT NULL, 'date' timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY ('id') ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=168580 ;

"" ""

Пример данных: https://jpst.it/1bfFt

Текущий выход: точка данных ooscount и дата каждые 5 минут (т. data: [{"ooscount":"4907","date":"2018-02-21 09:40:01"},{"ooscount":"4905","date":"2018-02-21 09:35:02"},{"ooscount":"4910","date":"2018-02-21 09:30:02"},{"ooscount":"4904","date":"2018-02-21 09:25:01"},{"ooscount":"4900","date":"2018-02-21 09:20:02"},{"ooscount":"4898","date":"2018-02-21 09:15:02"},{"ooscount":"4989","date":"2018-02-21 09:10:01"},{"ooscount":"5008","date":"2018-02-21 09:05:02"},{"ooscount":"4933","date":"2018-02-21 09:00:01"},{"ooscount":"4915","date":"2018-02-21 08:55:01"},{"ooscount":"4903","date":"2018-02-21 08:50:02"},{"ooscount":"4898","date":"2018-02-21 08:45:01"},{"ooscount":"4899","date":"2018-02-21 08:40:01"},{"ooscount":"4909","date":"2018-02-21 08:35:01"},{"ooscount":"4918","date":"2018-02-21 08:30:01"},{"ooscount":"4906","date":"2018-02-21 08:25:02"},{"ooscount":"4906","date":"2018-02-21 08:20:01"},{"ooscount":"4900","date":"2018-02-21 08:15:02"},{"ooscount":"4895","date":"2018-02-21 08:10:01"},{"ooscount":"4883","date":"2018-02-21 08:05:02"},{"ooscount":"4881","date":"2018-02-21 08:00:01"},{"ooscount":"4879","date":"2018-02-21 07:55:02"},{"ooscount":"4883","date":"2018-02-21 07:50:02"},{"ooscount":"4875","date":"2018-02-21 07:45:02"},{"ooscount":"4875","date":"2018-02-21 07:40:01"},{"ooscount":"4879","date":"2018-02-21 07:35:02"},{"ooscount":"4882","date":"2018-02-21 07:30:01"},{"ooscount":"4888","date":"2018-02-21 07:25:01"},{"ooscount":"4877","date":"2018-02-21 07:20:01"},{"ooscount":"4879","date":"2018-02-21 07:15:02"},{"ooscount":"4884","date":"2018-02-21 07:10:02"},{"ooscount":"4886","date":"2018-02-21 07:05:02"},{"ooscount":"4904","date":"2018-02-21 07:00:02"},{"ooscount":"4906","date":"2018-02-21 06:55:01"},{"ooscount":"4904","date":"2018-02-21 06:53:32"},{"ooscount":"4904","date":"2018-02-21 06:50:02"},{"ooscount":"4892","date":"2018-02-21 06:45:01"},{"ooscount":"4795","date":"2018-02-21 06:40:02"},{"ooscount":"4793","date":"2018-02-21 06:35:01"},{"ooscount":"4799","date":"2018-02-21 06:30:02"},{"ooscount":"4797","date":"2018-02-21 06:25:02"},{"ooscount":"4802","date":"2018-02-21 06:20:01"},{"ooscount":"4801","date":"2018-02-21 06:15:01"},{"ooscount":"4792","date":"2018-02-21 06:10:02"},{"ooscount":"4798","date":"2018-02-21 06:05:02"},{"ooscount":"4797","date":"2018-02-21 06:00:01"},{"ooscount":"4798","date":"2018-02-21 05:55:02"},{"ooscount":"4794","date":"2018-02-21 05:50:01"},{"ooscount":"4796","date":"2018-02-21 05:45:02"},{"ooscount":"4804","date":"2018-02-21 05:40:02"},{"ooscount":"4803","date":"2018-02-21 05:35:01"},{"ooscount":"4809","date":"2018-02-21 05:30:02"},{"ooscount":"4811","date":"2018-02-21 05:25:01"},{"ooscount":"4810","date":"2018-02-21 05:20:01"},{"ooscount":"4831","date":"2018-02-21 05:15:02"},{"ooscount":"4839","date":"2018-02-21 05:10:02"},{"ooscount":"4859","date":"2018-02-21 05:05:01"},{"ooscount":"4859","date":"2018-02-21 05:00:01"},{"ooscount":"4858","date":"2018-02-21 04:55:02"},{"ooscount":"4858","date":"2018-02-21 04:50:02"},{"ooscount":"4863","date":"2018-02-21 04:45:02"},{"ooscount":"4868","date":"2018-02-21 04:40:01"},{"ooscount":"4872","date":"2018-02-21 04:35:01"},{"ooscount":"4868","date":"2018-02-21 04:30:02"},{"ooscount":"4867","date":"2018-02-21 04:25:02"},{"ooscount":"4870","date":"2018-02-21 04:20:01"},{"ooscount":"4866","date":"2018-02-21 04:15:02"},{"ooscount":"4864","date":"2018-02-21 04:10:02"},{"ooscount":"4863","date":"2018-02-21 04:05:01"},{"ooscount":"4874","date":"2018-02-21 04:00:02"},{"ooscount":"4881","date":"2018-02-21 03:55:01"},{"ooscount":"4850","date":"2018-02-21 03:50:02"},{"ooscount":"4846","date":"2018-02-21 03:45:01"},{"ooscount":"4847","date":"2018-02-21 03:40:02"},{"ooscount":"4850","date":"2018-02-21 03:35:02"},{"ooscount":"4845","date":"2018-02-21 03:30:01"},{"ooscount":"4847","date":"2018-02-21 03:25:02"},{"ooscount":"4848","date":"2018-02-21 03:20:01"},{"ooscount":"4847","date":"2018-02-21 03:15:02"},{"ooscount":"4852","date":"2018-02-21 03:10:03"},{"ooscount":"4854","date":"2018-02-21 03:05:01"},{"ooscount":"4864","date":"2018-02-21 03:00:01"},{"ooscount":"4867","date":"2018-02-21 02:55:02"},{"ooscount":"4868","date":"2018-02-21 02:50:01"},{"ooscount":"4862","date":"2018-02-21 02:45:02"}], data: [{"ooscount":"4907","date":"2018-02-21 09:40:01"},{"ooscount":"4905","date":"2018-02-21 09:35:02"},{"ooscount":"4910","date":"2018-02-21 09:30:02"},{"ooscount":"4904","date":"2018-02-21 09:25:01"},{"ooscount":"4900","date":"2018-02-21 09:20:02"},{"ooscount":"4898","date":"2018-02-21 09:15:02"},{"ooscount":"4989","date":"2018-02-21 09:10:01"},{"ooscount":"5008","date":"2018-02-21 09:05:02"},{"ooscount":"4933","date":"2018-02-21 09:00:01"},{"ooscount":"4915","date":"2018-02-21 08:55:01"},{"ooscount":"4903","date":"2018-02-21 08:50:02"},{"ooscount":"4898","date":"2018-02-21 08:45:01"},{"ooscount":"4899","date":"2018-02-21 08:40:01"},{"ooscount":"4909","date":"2018-02-21 08:35:01"},{"ooscount":"4918","date":"2018-02-21 08:30:01"},{"ooscount":"4906","date":"2018-02-21 08:25:02"},{"ooscount":"4906","date":"2018-02-21 08:20:01"},{"ooscount":"4900","date":"2018-02-21 08:15:02"},{"ooscount":"4895","date":"2018-02-21 08:10:01"},{"ooscount":"4883","date":"2018-02-21 08:05:02"},{"ooscount":"4881","date":"2018-02-21 08:00:01"},{"ooscount":"4879","date":"2018-02-21 07:55:02"},{"ooscount":"4883","date":"2018-02-21 07:50:02"},{"ooscount":"4875","date":"2018-02-21 07:45:02"},{"ooscount":"4875","date":"2018-02-21 07:40:01"},{"ooscount":"4879","date":"2018-02-21 07:35:02"},{"ooscount":"4882","date":"2018-02-21 07:30:01"},{"ooscount":"4888","date":"2018-02-21 07:25:01"},{"ooscount":"4877","date":"2018-02-21 07:20:01"},{"ooscount":"4879","date":"2018-02-21 07:15:02"},{"ooscount":"4884","date":"2018-02-21 07:10:02"},{"ooscount":"4886","date":"2018-02-21 07:05:02"},{"ooscount":"4904","date":"2018-02-21 07:00:02"},{"ooscount":"4906","date":"2018-02-21 06:55:01"},{"ooscount":"4904","date":"2018-02-21 06:53:32"},{"ooscount":"4904","date":"2018-02-21 06:50:02"},{"ooscount":"4892","date":"2018-02-21 06:45:01"},{"ooscount":"4795","date":"2018-02-21 06:40:02"},{"ooscount":"4793","date":"2018-02-21 06:35:01"},{"ooscount":"4799","date":"2018-02-21 06:30:02"},{"ooscount":"4797","date":"2018-02-21 06:25:02"},{"ooscount":"4802","date":"2018-02-21 06:20:01"},{"ooscount":"4801","date":"2018-02-21 06:15:01"},{"ooscount":"4792","date":"2018-02-21 06:10:02"},{"ooscount":"4798","date":"2018-02-21 06:05:02"},{"ooscount":"4797","date":"2018-02-21 06:00:01"},{"ooscount":"4798","date":"2018-02-21 05:55:02"},{"ooscount":"4794","date":"2018-02-21 05:50:01"},{"ooscount":"4796","date":"2018-02-21 05:45:02"},{"ooscount":"4804","date":"2018-02-21 05:40:02"},{"ooscount":"4803","date":"2018-02-21 05:35:01"},{"ooscount":"4809","date":"2018-02-21 05:30:02"},{"ooscount":"4811","date":"2018-02-21 05:25:01"},{"ooscount":"4810","date":"2018-02-21 05:20:01"},{"ooscount":"4831","date":"2018-02-21 05:15:02"},{"ooscount":"4839","date":"2018-02-21 05:10:02"},{"ooscount":"4859","date":"2018-02-21 05:05:01"},{"ooscount":"4859","date":"2018-02-21 05:00:01"},{"ooscount":"4858","date":"2018-02-21 04:55:02"},{"ooscount":"4858","date":"2018-02-21 04:50:02"},{"ooscount":"4863","date":"2018-02-21 04:45:02"},{"ooscount":"4868","date":"2018-02-21 04:40:01"},{"ooscount":"4872","date":"2018-02-21 04:35:01"},{"ooscount":"4868","date":"2018-02-21 04:30:02"},{"ooscount":"4867","date":"2018-02-21 04:25:02"},{"ooscount":"4870","date":"2018-02-21 04:20:01"},{"ooscount":"4866","date":"2018-02-21 04:15:02"},{"ooscount":"4864","date":"2018-02-21 04:10:02"},{"ooscount":"4863","date":"2018-02-21 04:05:01"},{"ooscount":"4874","date":"2018-02-21 04:00:02"},{"ooscount":"4881","date":"2018-02-21 03:55:01"},{"ooscount":"4850","date":"2018-02-21 03:50:02"},{"ooscount":"4846","date":"2018-02-21 03:45:01"},{"ooscount":"4847","date":"2018-02-21 03:40:02"},{"ooscount":"4850","date":"2018-02-21 03:35:02"},{"ooscount":"4845","date":"2018-02-21 03:30:01"},{"ooscount":"4847","date":"2018-02-21 03:25:02"},{"ooscount":"4848","date":"2018-02-21 03:20:01"},{"ooscount":"4847","date":"2018-02-21 03:15:02"},{"ooscount":"4852","date":"2018-02-21 03:10:03"},{"ooscount":"4854","date":"2018-02-21 03:05:01"},{"ooscount":"4864","date":"2018-02-21 03:00:01"},{"ooscount":"4867","date":"2018-02-21 02:55:02"},{"ooscount":"4868","date":"2018-02-21 02:50:01"},{"ooscount":"4862","date":"2018-02-21 02:45:02"}],

Цель состоит в том, чтобы иметь меньше точек данных за тот же промежуток времени.