Question

我在加入两个表的内容时遇到了一些麻烦。这是目前的情况：

买
文章 购买 年度
1 12400 2011
1 28000 2012
1 46351 2015

已售出
文章 已售出 年度
1 6400 2011
1 12000 2013
1 60900 2014

期望的结果
文章 购买 已售出 年
1 12400 6400 2011
1 28000 NULL 2012
1 NULL 12000 2013
1 NULL 60900 2014
1 46351 NULL 2015

我已尝试以下方法来达到预期效果：

SELECT b.article, b.bought, s.sold, b.year
FROM Bought AS b
  LEFT JOIN Sold as s ON s.article = b.article AND s.year = b.year
WHERE b.article = '1'
ORDER BY b.year

这仅返回2011年的结果（两个值均存在）。

使用包含所有文章的第三个表的另一个尝试返回了相同的错误结果，并且它有两年的列，这是不理想的：

SELECT art.article, b.bought, s.sold, b.year, s.year
FROM articles AS art
  LEFT OUTER JOIN bought AS b ON art.article = b.article
  LEFT OUTER JOIN Sold AS s ON art.article = s.article
     AND (b.year = s.year OR b.year IS NULL OR s.year IS NULL)
 WHERE art.article = '1'

我尝试在最后一个SQL语句中使用不同类型的连接，但它们似乎都不起作用。我怎样才能达到预期的效果？

Answer 1

听起来你想要full outer join：

SELECT coalesce(b.article, s.article) as article, b.bought, s.sold,
       coalesce(b.year, s.year) as year
FROM Bought b FULL OUTER JOIN
     Sold s
     ON s.article = b.article AND s.year = b.year
WHERE (b.article = '1' OR s.article = '1')
ORDER BY year

Answer 2

您应该使用full outer join：

select coalesce(b.article, s.article)
     , b.bought
     , s.sold
     , coalesce (b.year, s.year) as year
from Bought b
full join Sold s on s.article = b.article
                 and s.year = b.year
where coalesce(b.article, s.article) = '1'
order by year

Answer 3

你可以做一个工会。首先选择左连接，然后将已售出的结果合并到已购买的相应行中。

SELECT b.article, b.bought, s.sold, b.year
FROM Bought AS b
LEFT JOIN Sold as s ON s.article = b.article AND s.year = b.year
where article = 1
Union 
SELECT article,null, sold, year
FROM sold where article =1 and year not in (select year from bought)

这样的事情。我没有测试过，但你可以得到这个想法。

SQL在两个表

3 个答案: