Question

如何使用连接编写此查询？我试过这样做但它不起作用。

select fund.fundname, sum(shares) as tt, (sum(shares)*price.price) as value 
from trans, fund, customer, price 
where trans.fundid = fund.fundid 
and trans.transdate = '2009-1-1' 
and price.fundid = trans.fundid 
and price.pricedate = trans.transdate 
and trans.sin = customer.sin 
and customer.name = 'Jacob' 
group by fund.fundname, price.price;

由于

Answer 1

我想你在谈论显式的连接。就像你拥有它一样，连接只是隐含的。你这样做：

SELECT fund.fundname, sum(shares) as tt, (sum(shares)*price.price) as value 
FROM trans
JOIN fund
 ON ( trans.fundid = fund.fundid )
JOIN customer
 ON ( trans.sin = customer.sin )
JOIN price 
 ON ( price.fundid = trans.fundid )
WHERE trans.transdate = '2009-1-1' 
 AND price.pricedate = trans.transdate 
 AND customer.name = 'Jacob' 
GROUP BY fund.fundname, price.price;

Postgresql还允许使用USING的漂亮简写，其中只包含最终结果集中列的一个副本：

SELECT fundname, sum(shares) as tt, (sum(shares)*price.price) as value 
FROM trans
JOIN fund
 USING ( fundid )
JOIN customer
 USING ( sin )
JOIN price 
 USING ( fundid )
WHERE trans.transdate = '2009-1-1' 
 AND price.pricedate = trans.transdate 
 AND customer.name = 'Jacob' 
GROUP BY fund.fundname, price.price;

Answer 2

您只需要分离连接条件和过滤条件：

SELECT fund.fundname, SUM(shares) AS tt, SUM(shares) * price.price AS value
FROM trans
INNER JOIN fund
    USING (fundid)
INNER JOIN price
    ON price.fundid = trans.fundid
   AND price.pricedate = trans.transdate
INNER JOIN customer
    USING (sin)
WHERE transdate = '2009-1-1'
  AND customer.name = 'Jacob'
GROUP BY fund.fundname, price.price

请注意，USING将“合并”两列，因此您不必使用别名。

Answer 3

 select fund.fundname, sum(shares) as tt, (sum(shares)*price.price) as value 
 from trans 
 join fund on fund.fundid=trans.fundid 
 join customer on customer.sin=trans.sin 
 join price on price.pricedate=trans.transdate
 where  
 trans.transdate = '2009-1-1' 
 and customer.name = 'Jacob' 
 group by fund.fundname, price.price;

Answer 4

还有一个：

SELECT f.fundname
      ,sum(shares) AS tt
      ,(sum(shares) * p.price) AS value 
FROM   trans t
JOIN   fund f USING (fundid)
JOIN   price p ON (p.fundid, p.pricedate) = (t.fundid, t.transdate)
JOIN   customer c USING (sin)
WHERE  t.transdate = '2009-1-1' 
AND    c.name = 'Jacob' 
GROUP  BY 1, p.price;

我使用了一些语法简化：

USING如果左右两侧的名称相同。小心，如果名称多次弹出，那么JOINS的顺序会有所不同，或者可能会变得模棱两可。示例：sin。如果还有fund.sin，则必须使用明确的JOIN ON。
(p.fundid, p.pricedate) = (t.fundid, t.transdate)是
的简称 (p.fundid = t.fundid AND p.pricedate = t.transdate)
GROUP BY 1是 GROUP BY <fist column in the select list>

有关fine manual here中加入的详情。

PostgreSQL：如何使用连接编写查询？

4 个答案: