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
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