SQL 列出所有有实际所有者的公寓

Question

我正在尝试使用查询来列出具有实际所有者的所有公寓。

我的公寓table是这样的：

building | apartmentNbr | owner |      start |        end
      b1 |           a1 |    o1 | 2009-08-13 | 2010-08-13
      b1 |           a1 |    o2 | 2010-08-14 | 2019-01-01
      b1 |           a2 |    o3 | 2009-01-03 | 2010-01-03
      b1 |           a2 |    o4 | 2010-01-04 | 2010-08-13
      b1 |           a2 |    o5 | 2010-08-14 | 9999-12-31
      b1 |           a3 |    o6 | 2010-08-14 | 2019-12-31
      b1 |           a3 |    o7 | 2020-02-14 | 9999-12-31
      b2 |           b1 |    o8 | 2012-08-14 | 9999-12-31
...

我的查询

SELECT *
FROM Appartments
WHERE CURDATE() BETWEEN startDate AND endDate

我只有被占用的公寓，但我也想有这样的免费公寓：

building | apartmentNbr | owner
      b1 |           a1 |  null
      b1 |           a2 |    o5
      b1 |           a3 |  null
      b2 |           b1 |    o8

我该如何解决这个问题？

Answer 1

做一个GROUP BY。使用 case 表达式获取当前所有者（或 null）。

SELECT building, apartmentNbr,
       max(case when CURDATE() BETWEEN startDate AND endDate then owner end)
FROM Appartments
GROUP BY building, apartmentNbr

SQL 列出所有有实际所有者的公寓

SQL list all apartments with actual owner

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