SQL 嵌套连接不使用 WHERE

Question

目前每种产品的价格是多少？显示产品代码、产品描述、单位及其当前价格。始终假设并非所有产品都有单价，但即使没有单价，您也需要显示它。不使用 WHERE 脚本

产品表

1. 产品代码
2. 说明
3. 单位

价格表

1. 产品代码
2. effDate
3. 单价

这是我的工作...请帮助我改进我的答案。

SELECT p.prodCode, p.description, p.unit, MAX(ph.unitPrice)  "Current Price" 
FROM product p 
INNER JOIN priceHist AS ph 
ON p.prodCode = ph.prodCode
GROUP BY p.prodCode, p.description, p.unit
ORDER BY MAX(ph.unitPrice); 

有人说我需要两次使用 PRICEHIST

Answer 1

用户窗口函数和left join:

select . . . -- whatever columns you want
from products p left join
     (select ph.*,
             row_number() over (partition by p.prodcode order by effdate desc) as seqnum
      from pricehist ph
     ) ph
     on ph.prodcode = p.prodcode and ph.seqnum = 1;

Answer 2

试试这个：

SELECT a.prodCode, a.description, a.unit, SUM(b.unitPrice)
FROM ProductTable a
LEFT JOIN PriceHistTable b ON a.prodCode = b.prodCode
GROUP BY a.prodCode, a.description, a.unit, b.unitPrice

Answer 3

假设您想为prodCode 选择unitPrice 和最新 effDate，下面的查询应该可以工作。 cmets 中的解释。

select x.prodCode, x.description, x.unit, y.unitPrice
from Product x
left join (
   --- Create a table y with one row per (prodCode, effDate)
   --- choosing the latest effDate per prodCode
   select a.prodCode, a.effDate, a.unitPrice
   from PriceHist  a
   join (
       --- Create b as (prodCode, effDate)
       select prodCode, max(effDate) as maxEffDate
       from PriceHist
       group by prodCode
   ) b
   on a.prodCode = b.prodCode and a.effDate = b.maxEffDate
) y
on x.prodCode = y.prodCode