Question

Say I have two tables: cat_collection and cat_mapping

cat_mapping contains three fields; id, collection_id, and post_id

I would like to be able to select all names from cat_collection

SELECT name FROM cat_collection

as well as the number of times they are referenced in cat_mapping

So if cat_collection contained

| id |   | name |
  0        cat1
  1        cat2

and cat_mapping contained

| id |   | collection_id |   | post_id |
  0              1               0
  1              1               1

how can I return

| name |   | count |
  cat1        0
  cat2        2

---

solution

SELECT cc.name, (

SELECT COUNT( cm.collection_id )
FROM cat_mapping AS cm
WHERE cm.collection_id = cc.id
) AS `count`
FROM cat_collection AS cc

Answer 1

I think a subquery like this would do it:

SELECT cc.name, (SELECT COUNT(cm.id) FROM cat_mapping cm WHERE cm.collection_id = cc.id) AS cnt
FROM cat_collection cc