How to get Postgres to return 0 for empty rows

I have a query which get data summarised between two dates like so:

SELECT date(created_at),
COUNT(COALESCE(id, 0))                                                                      AS total_orders,
   SUM(COALESCE(total_price, 0))                                                               AS total_price,
   SUM(COALESCE(taxes, 0))                                                                     AS taxes,
   SUM(COALESCE(shipping, 0))                                                                  AS shipping,
   AVG(COALESCE(total_price, 0))                                                               AS average_order_value,
   SUM(COALESCE(total_discount, 0))                                                            AS total_discount,
   SUM(total_price - COALESCE(taxes, 0) - COALESCE(shipping, 0) - COALESCE(total_discount, 0)) as net_sales
FROM orders
WHERE shop_id = 43
  AND orders.active = true
  AND orders.created_at >= '2022-07-20'
  AND orders.created_at <= '2022-07-26'
GROUP BY date (created_at)
order by created_at::date desc

However for dates that do not have any orders, the query returns nothing and I’d like to return 0.

I have tried with COALESCE but that doesn’t seem to do the trick?

Any suggestions?

Answer

Please refer to the below script.

SELECT *
FROM 
    (SELECT date(created_at) AS created_at,
         COUNT(id) AS total_orders,
         SUM(total_price) AS total_price,
         SUM(taxes) AS taxes,
         SUM(shipping) AS shipping,
         AVG(total_price) AS average_order_value,
         SUM(total_discount) AS total_discount,
         SUM(total_price - taxes - shipping - total_discount) AS net_sales
    FROM orders
    WHERE shop_id = 43
        AND orders.active = true
        AND orders.created_at >= '2022-07-20'
        AND orders.created_at <= '2022-07-26'
    GROUP BY  date (created_at)
UNION
SELECT dates AS created_at,
         0 AS total_orders,
         0 AS total_price,
         0 AS taxes,
         0 AS shipping,
         0 AS average_order_value,
         0 AS total_discount,
         0 AS net_sales
FROM generate_series('2022-07-20', '2022-07-26', interval '1 day') AS dates
WHERE dates NOT IN 
    (SELECT created_at
    FROM orders
    WHERE shop_id = 43
        AND orders.active = true
        AND orders.created_at >= '2022-07-20'
        AND orders.created_at <= '2022-07-26' ) ) a
ORDER BY  created_at::date desc;

There is one sample for your reference. Sample

I got your duplicate test cases at my side. The root cause is created_at field (datattype:timestamp), hence there are duplicate lines.

Below script is correct for your request.

SELECT *
FROM 
    (SELECT date(created_at) AS created_at,
         COUNT(id) AS total_orders,
         SUM(total_price) AS total_price,
         SUM(taxes) AS taxes,
         SUM(shipping) AS shipping,
         AVG(total_price) AS average_order_value,
         SUM(total_discount) AS total_discount,
         SUM(total_price - taxes - shipping - total_discount) AS net_sales
    FROM orders
    WHERE shop_id = 43
        AND orders.active = true
        AND orders.created_at >= '2022-07-20'
        AND orders.created_at <= '2022-07-26'
    GROUP BY  date (created_at)
UNION
SELECT dates AS created_at,
         0 AS total_orders,
         0 AS total_price,
         0 AS taxes,
         0 AS shipping,
         0 AS average_order_value,
         0 AS total_discount,
         0 AS net_sales
FROM generate_series('2022-07-20', '2022-07-26', interval '1 day') AS dates
WHERE dates NOT IN 
    (SELECT date (created_at)
    FROM orders
    WHERE shop_id = 43
        AND orders.active = true
        AND orders.created_at >= '2022-07-20'
        AND orders.created_at <= '2022-07-26' ) ) a
ORDER BY  created_at::date desc;

Here is a sample that’s same with your side. Link