PostgreSQL带WHERE子句的generate_series

Question

I'm having an issue generating a series of dates and then returning the COUNT of rows matching that each date in the series.

SELECT generate_series(current_date - interval '30 days', current_date, '1 day':: interval) AS i, COUNT(*)
FROM download
WHERE product_uuid = 'someUUID'
AND created_at = i
GROUP BY created_at::date
ORDER BY created_at::date ASC

I want the output to be the number of rows that match the current date in the series.

05-05-2018, 35
05-06-2018, 23
05-07-2018, 0
05-08-2018, 10
...

The schema has the following columns: id , product_uuid , created_at . Any help would be greatly appreciated. I can add more detail if needed.

Answer 1

Put the table generating function in the from and use a join :

SELECT g.dte, COUNT(d.product_uuid)
FROM generate_series(current_date - interval '30 days', current_date, '1 day':: interval
                    ) gs(dte) left join
     download d
     on d.product_uuid = 'someUUID' AND
        d.created_at::date = g.dte
GROUP BY g.dte
ORDER BY g.dte;