您可以将 3 个 CTE 合二为一吗？

Question

我有一个用 3 个 CTE 编写的查询，我需要仅使用 1 个 CTE 来获得完全相同的结果。有人可以帮助我吗？

WITH Q1(cid, sumEP) AS
(
    SELECT customerid, SUM(Extendedprice) 
    From "Invoices" 
    GROUP BY customerid 
), Q2(cid, oid, mf) AS 
(
    SELECT DISTINCT customerid, orderid, freight 
    FROM "Invoices" 
), Q3 AS 
( 
    SELECT cid, SUM(mf) AS smf 
    FROM Q2 
    GROUP BY cid 
)
SELECT Q1.cid, sumEP + smf AS total 
FROM Q1 
JOIN Q3 ON Q1.cid = Q3.cid 
LIMIT 10

Answer 1

smf 是每个订单（对于同一客户）的 freight 不同值的总和，但是您可以使用 sum(distinct freight)

所以我会建议这个查询：

WITH Q(customerid, orderid, total) AS 
(
    SELECT   customerid, orderid, SUM(Extendedprice) + SUM(DISTINCT freight)
    FROM     Invoices
    GROUP BY customerid, orderid 
)
SELECT customerid, SUM(total) AS total
FROM   Q
GROUP BY customerid
ORDER BY 2 DESC
LIMIT 10;

当不存在同一客户的不同订单运费相同的情况时，则可以简化为：

SELECT   customerid, SUM(Extendedprice) + SUM(DISTINCT freight) AS total
FROM     Invoices
GROUP BY customerid 
ORDER BY 2 DESC 
LIMIT 10

请注意，我添加了一个 order by，这样您就可以用它背后的一些逻辑来限制结果——在本例中，总计排名前 10。根据需要更改。

您可以将 3 个 CTE 合二为一吗？

Can you combine 3 CTE's into one?

sql

common-table-expression