K，所以我有两个表：

categories
+----+----------+
| id | slug     |
+----+----------+
| 1  | billing  |
| 2  | security |
| 3  | people   |
| 4  | privacy  |
| 5  | messages |
+----+----------+

categories_questions
+------------------+-------------+
| id | question_id | category_id |
+------------------+-------------+
| 1  |           1 |           2 |
| 2  |           2 |           5 |
| 3  |           3 |           2 |
| 4  |           4 |           4 |
| 5  |           4 |           2 |
| 6  |           5 |           4 |
+------------------+-------------+

我想从类别中获取所有信息，并计算每个类别中的问题数（question_id）。

假设，第一个类别（计费）将有一个问题，第二个类别（安全）将有3个问题。

我已经试过了：

SELECT categories.*, count(categories_questions.id) AS numberOfQuestions
FROM categories
INNER JOIN categories_questions
ON categories.id = categories_questions.category_id