如何获取列中每个不同值的计数? [英] How to get the count of each distinct value in a column?
问题描述
我有一个称为"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.我该如何计算每个类别在一个SQL查询中全部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,这样的查询可能返回如下符号数组:(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帖子WHERE category =#
,然后将返回值组合到最终数组中.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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