Question

I have a table called categories and a table called business_categories_coupling. In Categories, you have the usual id, name, parent. In the Coupling table, you have business_id and category_id. Each business can have multiple categories, so I store them in that table. It kinda looks like this:

business_id    category_id
73             80
73             81
73             90
74             4
74             10

Right now, my query is just selecting all the categories, doing a foreach and doing a db query in each loop to find how many businesses are in that category. Obviously not the right way to go about it.

Is there a way to do a SQL query that basically selects all the categories, gets the number of times it comes up in the coupling table, and add a count to each category?

SELECT
    C.*
FROM
    CATEGORIES AS C
LEFT JOIN
    BUSINESS_CATEGORIES_COUPLING AS B
ON
    C.id = B.category_id;

Kinda like that, but with a count somewhere. I’ve tried various setups but nothing works like I want. Any suggestions?

EDIT 1

Solution as provided by @phani-rahul, but I added a WHERE clause:

SELECT cat.id AS id, cat.name AS name, cat.slug AS slug, COUNT(cat.id) AS business_count
FROM categories AS cat
LEFT JOIN business_categories_coupling AS coupling ON cat.id=coupling.category_id
WHERE coupling.category_id IS NOT NULL
GROUP BY cat.id

Answer 1

Yes, there is.
you can use Group by clause:

select a.id as category, count(a.id) as count_of_category
from categories a
left join business_categories_coupling b on a.id=b.category_id
group by a.id

your result would be something like:

category   count_of_category
80          2
81          5
90          1
.           .
.           .
.           .