如何获取列中每个不同值的计数?

How to get the count of each distinct value in a column?(如何获取列中每个不同值的计数?)

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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