sql - 如何访问 Postgres hstore 字段中的数据并从 Active Record 求和

Question

我有一个 Postgres 9.3.5 数据库，其中有一个名为 order_items 的表。数据布局如下。

 id | product_sku(character var) | qty_ordered(integer) | item_price(hstore)
1   | 9AYSNL                     | 1                    |"Amount"=>"5.99", "CurrencyCode"=>"USD"
2   | 9AYSNL                     | 1                    |"Amount"=>"5.99", "CurrencyCode"=>"USD"
3   | 9AYSNL                     | 2                    |"Amount"=>"11.98", "CurrencyCode"=>"USD"
4   | 9AYSNL                     | 1                    |"Amount"=>"5.99", "CurrencyCode"=>"USD"
5   | EZAY1D                     | 1                    |"Amount"=>"21.98", "CurrencyCode"=>"USD"

我想做的是找出每个 product_sku 在表中出现的频率以及该产品的总“数量”。

如果我运行以下命令，我会得到这个结果。

products =  OrderItem.where('quantity_ordered > 0').group(:product_sku).count

{"9AYSNL"=>4,
"EZAY1D"=>1}

我想以某种方式返回如下内容(total_orders 是 product_sku 在表中的次数，而不是订购的数量)。我想按 total_orders 返回前 20 名。

[{product_sku: "9AYSNL", total_orders: 4, total_order_amount: "29.95"},
 {product_sku: "EZAY1D", total_orders: 1, total_order_amount: "21.98"}]

Answer 1

要获得基本结果:

SELECT product_sku
     , count(*) AS total_orders
     , sum((item_price->'Amount')::numeric) AS total_order_amount
FROM   orderitem
WHERE  qty_ordered > 0
GROUP  BY product_sku
ORDER  BY count(*) DESC
LIMIT  20;  -- get only top 20

要像您显示的那样以 JSON 数组形式获取结果:

SELECT json_agg(t)
FROM  (
   SELECT product_sku
        , count(*) AS total_orders
        , sum((item_price->'Amount')::numeric) AS total_order_amount
   FROM   orderitem
   WHERE  qty_ordered > 0
   GROUP  BY product_sku
   ORDER  BY count(*) DESC
   LIMIT  20
   ) t;

SQL fiddle.