Postgres: Date grouping in Subquery from timestamp

Question

I am trying find out how many leads are generated per listing per day.

I have this query:

SELECT 
    vl.listing_id,
    vl.created_at::date as dt,
    (
        SELECT count(*) 
        FROM voice_leads vl2
        WHERE vl2.listing_id = vl.listing_id 
        AND vl.created_at::date = vl2.created_at::date
    ) as cnt
FROM voice_leads vl
GROUP BY listing_id, vl.created_at::date
ORDER BY listing_id

but when executing I get "ERROR: subquery uses ungrouped column "vl.created_at" from outer query LINE 8: AND vl.created_at::date = vl2.created_at::date"

Any idea on what I could do to fix it?

Answer 1

SELECT 
    vl.listing_id,
    vl.created_at::date as dt,
    count(cnt.*)
FROM voice_leads vl, lateral (SELECT *
        from voice_leads vl2
        WHERE vl2.listing_id = vl.listing_id 
        AND vl.created_at::date = vl2.created_at::date) cnt
GROUP BY vl.listing_id, vl.created_at::date
ORDER BY listing_id

Answer 2

You don't need the subquery:

SELECT 
    vl.listing_id,
    vl.created_at::date as dt,
    count( vl.listing_id ) as cnt
FROM voice_leads vl
GROUP BY listing_id, vl.created_at::date
ORDER BY listing_id

should do the same.

count(field) will count the number of rows in each group.

count(*) will count the total number of rows.