sql - 前 3 个月的总和

Question

我很难从 12 月(上个月第 3 个月)获取行。我正在尝试计算特定时间段内销售的产品数量。这是我当前的查询:

 SELECT
   a.id,
   a.default_code,
(
   SELECT SUM(product_uom_qty) 
   AS 
   "Total Sold" 
   FROM 
   sale_order_line c 
   WHERE 
   c.product_id = a.id
),
(
   SELECT SUM(product_uom_qty) 
   AS 
   "Month 3" 
   FROM sale_order_line c 
   WHERE
   c.product_id = a.id
   AND 
   MONTH(c.create_date) = MONTH(CURRENT_DATE - INTERVAL '3 Months')
   AND
   YEAR(c.create_date) = YEAR(CURRENT_DATE - INTERVAL '3 Months')
)
FROM
   product_product a 

这是数据库的样子:

sale_order_line

product_id product_uom_qty  create_date
33         230              2014-07-01 16:47:45.294313

product_product

id  default_code 
33  WHDXEB33

这是我收到的错误:

ERROR:  function month(timestamp without time zone) does not exist
LINE 21:    MONTH(c.create_date) = MONTH(CURRENT_DATE - INTERVAL

有什么可以帮助我指明正确的方向吗？

Answer 1

使用date_trunc()计算时间戳边界:

SELECT id, default_code
    , (SELECT SUM(product_uom_qty)
        FROM   sale_order_line c 
        WHERE  c.product_id = a.id
       ) AS "Total Sold" 
    , (SELECT SUM(product_uom_qty)
        FROM   sale_order_line c 
        WHERE  c.product_id = a.id
        AND    c.create_date >= date_trunc('month', now()) - interval '2 month'
        AND    c.create_date <  date_trunc('month', now()) - interval '1 month'
      ) AS "Month 3"
FROM   product_product a;

要获得十二月(现在是二月)，请使用这些表达式:

    AND    c.create_date >= date_trunc('month', now()) - interval '2 month'
    AND    c.create_date <  date_trunc('month', now()) - interval '1 month'

date_trunc('month', now()) 产生“2015-02-01 00:00”，减去 2 个月后得到“2014-12-01 00:00”。所以，“3 个月”可能是骗人的。

此外，请务必使用 sargable表达式 like demonstrated 以获得更快的性能并允许使用索引。

备选方案

根据您实际的数据库设计和数据分布，这可能会更快:

SELECT a.id, a.default_code, c."Total Sold", c."Month 3"
FROM   product_product a
LEFT  JOIN (
   SELECT product_id AS id
        , SUM(product_uom_qty) AS "Total Sold"
        , SUM(CASE WHEN c.create_date >= date_trunc('month', now()) - interval '2 month'
                   AND  c.create_date <  date_trunc('month', now()) - interval '1 month'
              THEN product_uom_qty ELSE 0 END) AS "Month 3" 
   FROM   sale_order_line
   GROUP  BY 1
   ) c USING (id);

由于您要选择所有行，这可能比相关子查询更快。在您加入之前， 进行汇总，这样更便宜。
但是，在选择单个或少数产品时，这实际上可能会慢!比较:

• Aggregate a single column in query with many columns
• Optimize GROUP BY query to retrieve latest record per user

或者在 Postgres 9.4+ 中使用 FILTER 子句:

...
        , SUM(product_uom_qty) 
             FILTER (WHERE c.create_date >= date_trunc('month', now()) - interval '2 month'
                     AND   c.create_date <  date_trunc('month', now()) - interval '1 month'
                    ) AS "Month 3"
...

详细信息:

• Select multiple row values into single row with multi-table clauses