Postgres 查询结果到 json 对象

Question

我的查询如下

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;

这给了我这样的结果：

我想要{"payload:"[payload1,payload2,payload3],"rowcount":n}。

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Postgres 10.3版，payload数据类型为jsonb

Answer 1

COALESCE(NULL, w.delivery_date)归结为只是w.delivery_date。

因此WHERE w.delivery_date = COALESCE(NULL, w.delivery_date)归结为WHERE w.delivery_date IS NOT NULL.

Count('payload') OVER () AS ROWCOUNT只是一种嘈杂的说法count(*) OVER () AS rowcount，并返回结果的总行数。

您当前的查询已简化：

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;

要获取像更新问题中那样的 JSON 对象，其中包含一个 JSON 对象数组和总行数：

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;

• 在应用 LIMIT 之前获取结果计数的最佳方法

如果您正在处理很多LIMIT行，则/ 的性能会OFFSET降低。考虑更复杂的分页技术：

• 在大表上使用 OFFSET 优化查询