查询MySQL计数数据并转换为JSON

My table contains a column of 'datetimes', with an id.

+----+---------------------+
| id |      datetime       |
+----+---------------------+
| 0  | 2016-09-02 12:13:13 |
| 1  | 2016-09-02 10:16:11 |
| 2  | 2016-09-05 11:03:23 |
| 3  | 2016-09-08 11:34:45 |
| 4  | 2016-09-08 09:23:06 |
| 5  | 2016-09-08 10:22:05 |
| .. |         ...         |
+----+---------------------+

There will be multiple instances of each date in the table. My aim is to gather the amount of times each date occurs. So for the table above:

2016-09-02 => 2
2016-09-05 => 1
2016-09-08 => 3

I then need to move the data into JSON format using PHP like so:

[{"date":"2016-09-02","count":"2"},
 {"date":"2016-09-05","count":"1"},
 {"date":"2016-09-08","count":"3"}]

The JSON format will be used by a d3.js script I have written to plot each date against the frequency each date occurs.

I have never dealt with this kind of query before so I really have no idea where to start, or how to use PHP to move into JSON format. Thank you to anyone that can help.

Use the following query:

SELECT DATE_FORMAT(datetime, '%Y-%m-%d') AS `date`,
       COUNT(*) AS `count`
FROM yourTable
GROUP BY DATE_FORMAT(datetime, '%Y-%m-%d')

Then create the JSON in your PHP code:

$a = array();
while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
    $a[] = array('date' => "$row['date']", 'count' => "$row['count']");
}

$json = json_encode($a);

I think below SQL useful to you. please run and see

SELECT  DATE_FORMAT(datetime, '%Y-%m-%d'),count(*)
FROM yourTable
GROUP BY 1
order by 1