Postgres query result to json object

Question

My query is given below

SELECT w.payload,
       Count('payload') OVER () AS ROWCOUNT
FROM wholesale_confirmation.wholesale_order_confirmation w
WHERE w.delivery_date = COALESCE(NULL, w.delivery_date)
  AND w.ship_to_location_id = COALESCE(NULL, w.ship_to_location_id)
  AND w.order_raised_date = COALESCE(NULL, w.order_raised_date)
  AND w.ship_from_location_id = COALESCE(NULL, w.ship_from_location_id)
LIMIT 10
OFFSET 0;

which is giving me result like this:

I want instead {"payload:"[payload1,payload2,payload3],"rowcount":n}.

---

Postgres version 10.3, payload data type is jsonb

Answer 1

COALESCE(NULL, w.delivery_date) boils down to just w.delivery_date.

Consequently WHERE w.delivery_date = COALESCE(NULL, w.delivery_date) boils down to WHERE w.delivery_date IS NOT NULL.

Count('payload') OVER () AS ROWCOUNT is just a noisy way of saying count(*) OVER () AS rowcount and returns the total row count of the result.

Your current query, simplified:

SELECT payload, count(*) OVER () AS rowcount
FROM   wholesale_confirmation.wholesale_order_confirmation
WHERE  delivery_date          IS NOT NULL
AND    ship_to_location_id    IS NOT NULL
AND    order_raised_date      IS NOT NULL
AND    ship_from_location_id  IS NOT NULL
LIMIT  10;

To get a JSON object like in your updated question, containing one array of JSON objects and the total count of rows:

SELECT json_build_object('payload', jsonb_agg(payload), 'rowcount', min(rowcount))
FROM  (
   SELECT payload, count(*) OVER () AS rowcount
   FROM   wholesale_confirmation.wholesale_order_confirmation
   WHERE  delivery_date          IS NOT NULL
   AND    ship_to_location_id    IS NOT NULL
   AND    order_raised_date      IS NOT NULL
   AND    ship_from_location_id  IS NOT NULL
   LIMIT  10
   ) sub;

• Best way to get result count before LIMIT was applied

If you are dealing with many rows, the performance with LIMIT / OFFSET degrades. Consider a more sophisticated pagination technique:

• Optimize query with OFFSET on large table

Answer 2

Use json_build_object:

WITH foobar AS ( 
SELECT w.payload,
       Count('payload') OVER () AS ROWCOUNT
FROM wholesale_confirmation.wholesale_order_confirmation w
WHERE w.delivery_date = COALESCE(NULL, w.delivery_date)
  AND w.ship_to_location_id = COALESCE(NULL, w.ship_to_location_id)
  AND w.order_raised_date = COALESCE(NULL, w.order_raised_date)
  AND w.ship_from_location_id = COALESCE(NULL, w.ship_from_location_id)
LIMIT 10
OFFSET 0
)

SELECT 
    json_build_object('payload', payload, 'rowcount', rowcount)
FROM 
    foobar