查询：

SELECT date, COUNT(*) AS Total
    FROM posts
    WHERE id_user = 7
    GROUP BY date

输出：

date       | Total
-----------------
2018-11-12 | 2
2018-11-13 | 4
2018-11-14 | 1
2018-11-15 | 5
2018-11-16 | 7

更新：
如果您想更改日期格式，请使用以下代码，

SELECT DATE_FORMAT(date, "%d/%m/%Y") As date, COUNT(*) AS Total
        FROM posts
        WHERE id_user = 7
        GROUP BY date

输出：

date       | Total
-----------------
12/11/2018 | 2
13/11/2018 | 4
14/11/2018 | 1
15/11/2018 | 5
16/11/2018 | 7

您没有在查询中输出日期，也没有对结果进行调整 id_user . 试试这个：

SELECT `date`, COUNT(*)
FROM posts
WHERE id_user = 7
GROUP BY `date`

输出

date        COUNT(*)
2018-11-12  2
2018-11-13  4
2018-11-14  1
2018-11-15  5
2018-11-16  7

在dbfiddle上演示