如何 select 表中的所有条目，其中子查询按第一个查询中的 id 计数另一个表中的条目

Question

I have two tables: albums and photos

albums

id	name	user_id
1	New Year 2022	2
2	Birthday Party	2
3	Wedding	2

For every album there are photos in photos table

photos

id	album_id	name
1	1	IMG_0754.JPG
2	2	IMG_0764.JPG
3	2	IMG_0654.JPG
4	3	IMG_1254.JPG
5	3	IMG_0054.JPG
6	3	IMG_0004.JPG

I need to select all albums by user_id (in this example by user_id 2) from albums table, and count all photos from photos table, so that I get something like

id	name	user_id	photo_count
1	New Year 2022	2	1
2	Birthday Party	2	2
3	Wedding	2	3

Thanks!

Answer 1

This is how I would write it with ms-sql. You may need to tweak it for postgresql.

SELECT a.id, a.name, a.user_id, count(*) as photo_count
FROM ALBUMS a
INNER JOIN PHOTOS p on a.id = p.id
GROUP BY a.id, a.name, a.user_id

Answer 2

I figured out the answer, which is

select albums.id, albums.name, albums.user_id,(select count(*) from photos where photos.album_id = albums.id) as photo_count from albums where user_id = 2

Answer 3

OK, after the advice of @Sonyck the solution would be

SELECT albums.id, albums.name, albums.user_id, count(*) as photo_count 
FROM albums 
JOIN photos ON (photos.album_id = albums.id)
WHERE user_id = 2
GROUP BY albums.id, albums.name, albums.user_id