问题描述
我有一个名为posts"的 SQL 表.看起来像这样:
I have an SQL table called "posts" that looks like this:
id | category
-----------------------
1 | 3
2 | 1
3 | 4
4 | 2
5 | 1
6 | 1
7 | 2
每个类别编号对应一个类别.我将如何计算一个 SQL 查询中每个类别出现在帖子中的次数?
Each category number corresponds to a category. How would I go about counting the number of times each category appears on a post all in one SQL query?
例如，这样的查询可能会返回一个符号数组，例如:(1:3, 2:2, 3:1, 4:1)
As an example, such a query might return a symbolic array such as this: (1:3, 2:2, 3:1, 4:1)
我目前的方法是对每个可能的类别使用查询，例如:SELECT COUNT(*) AS num FROM posts WHERE category=#，然后将返回值组合成一个最终的数组.但是，我正在寻找一种仅使用一个查询的解决方案.
My current method is to use queries for each possible category, such as: SELECT COUNT(*) AS num FROM posts WHERE category=#, and then combine the return values into a final array. However, I'm looking for a solution that uses only one query.
推荐答案
SELECT
category,
COUNT(*) AS `num`
FROM
posts
GROUP BY
category
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