两个查询的左外连接条件？

Question

我有以下两个查询来查找从 2014 年 1 月开始的每周的综合浏览量和订单。

select productid,
EXTRACT (week from dt)as WEEK,
count(productid)as PageViews
from PageView
where client = 'XYZ'
and dt between '2014-06-01' and '2014-06-30'
GROUP BY WEEK, productid
ORDER BY WEEK asc;

和

select
count(distinct t.orderid),
EXTRACT(week from t.dt) AS WEEK
FROM Transaction t
where t.client = 'XYZ'
and t.dt between '2014-01-01' AND '2014-06-30'
GROUP BY WEEK
ORDER BY WEEK asc;

为了获得正确的数据，我需要创建一个与 Transaction 和 PageView Tables 中的周匹配的连接条件，例如来自 Transaction 的周 = 来自 PageView 的周。然而，我不知道它的语法是什么样的。

做一个简单的

PageView pv LEFT OUTER JOIN Transaction t
ON pv.productid = t.productid 
AND EXTRACT(week from t.dt) = EXTRACT(week from pv.dt) 

没有给出正确的输出（即网页浏览量和订单量显着增加）。有人可以解释一下如何将这两个查询结合起来获得所需的输出，即 PageView 表中的所有产品和按周分组的 Transaction 表中的相应订单

Answer 1

select week, pid, pageviews, orders
from
    (
        select
            date_trunc('week', dt) as week,
            productid as pid,
            count(productid) as pageviews
        from pageview
        where client = 'XYZ' and dt between '2014-06-01' and '2014-06-30'
        group by 1, 2
    ) pv
    full outer join
    (
        select
            date_trunc('week', dt) as week,
            product_id as pid,
            count(orderid) as orders
        from transaction
        where client = 'XYZ' and dt between '2014-01-01' and '2014-06-30'
        group by 1, 2
    ) t using (week, pid)
order by 1, 2

Answer 2

我认为问题出在ON pv.productid = t.productid AND EXTRACT(week from t.dt) = EXTRACT(week from pv.dt)

这不能是左连接。 PV 和 T 之间的 ID 可能匹配，但在某些情况下周可能为空。所以 AND 会消除左连接。

因此，您只需先加入 ID，就可以得到笛卡尔坐标。然后，您需要过滤掉不匹配的周，但保留 T.Null 值。但是它假定 t.dt 不能为空，如果它可以为空，则计数可能仍会关闭，具体取决于您想要的方式处理事务表日期中的空值。

此外，您可能需要使用内联视图（但我认为这是矫枉过正）

SELECT * 
FROM
(select productid,
  EXTRACT (week from dt)as WEEK,
  count(productid)as PageViews
  from PageView
  where client = 'XYZ'
  and dt between '2014-06-01' and '2014-06-30'
  GROUP BY WEEK, productid) PV
LEFT JOIN (
  SELECT
  count(distinct t.orderid),
  EXTRACT(week from t.dt) AS WEEK
  FROM Transaction t
  where t.client = 'XYZ'
  and t.dt between '2014-01-01' AND '2014-06-30'
  GROUP BY WEEK) T
ON pv.productid = t.productid  --The gold is in this and the next line
WHERE (T.Week = PV.Week OR T.Week is null)  --don't forget this one.

我认为这行不通... 开启（PV.ProductID=T.productID 和 T.Week=PV.Week） 或（PV.ProductID = T.ProductID AND T.Week 为空）

因为尚未生成笛卡尔坐标系，因此尚未评估 T.Week。这就是为什么我认为它属于 where。