PostgreSQL：如何使用连接编写查询？

我该如何使用连接编写此查询？我试图去做，但它不起作用。PostgreSQL：如何使用连接编写查询？

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;

感谢

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2011-11-08 night mare

这是连接，甚至三个。可能甚至是交叉连接。你有什么尝试，为什么没有工作？错误讯息？ – stefan

我想你在谈论明确连接。就像你所拥有的那样，连接只是隐含的。你会做这样的：

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的还允许USING一个漂亮的简写，这将只包括在最终的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;

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2011-11-08 23:59:17

谢谢..我试图对它进行自然连接。常规连接和自然连接有区别吗？我的语法错了，我相信...... –

'NATURAL' JOINS将加入每个相似命名的列。 –

天然连接没有什么自然的。 – stefan

你一定要分开连接条件和筛选条件：

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会“合并”两列，因此您不必使用别名。

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2011-11-09 00:00:20

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;

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2011-11-09 00:01:22 Icarus

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，右功能相同的名称。小心，如果该名称弹出多次，那么JOINS的顺序会有所不同，或者它可能会变得模糊不清。示例：sin。如果还有fund.sin，则必须改为使用显式JOIN ON。
(p.fundid, p.pricedate) = (t.fundid, t.transdate)是短期的
(p.fundid = t.fundid AND p.pricedate = t.transdate)
GROUP BY 1 IST简称
GROUP BY <fist column in the select list>

更多有关fine manual here连接。

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2011-11-09 00:30:00

PostgreSQL：如何使用连接编写查询？

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