如何仅使用3个表中的SQL获取摘要

Question

I have 3 tables:

Table posts
    post_id
    category_id
    title

Table visits
    visit_id
    post_id
    visit_date

Table categories
    category_id
    category_name

I need to get something like this (assuming that table visits has 10 rows)

Category 1 (categories.category_name) / visits(count) = 5
Category 2 (categories.category_name) / visits(count) = 1
Category 3 (categories.category_name) / visits(count) = 4

How can I get a similar result using only MySQL?

I tried with INNERs, no success

Answer 1

It's a simple query. You need to join all three tables, and finally group the result by category name. It should look like:

select
  c.category_name, 
  count(*)
from categories c
join posts p on p.categoryid = c.category_id
join visits v on v.post_id = p.post_id
group by c.category_name
order by c.category_name