SQL：如何获取列中每个不同值的计数？ [英] SQL: How to get the count of each distinct value in a column?

问题描述

我有一个名为posts的SQL表，如下所示：

I have a 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。我如何计算每个类别在一个sql查询中出现的次数？

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，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)

我当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 = ＃，然后将返回值合并到最终数组中。但是，我正在寻找只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

这篇关于SQL：如何获取列中每个不同值的计数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！