Question

我的数据库中有两个表，一个用于离开飞机，另一个用于到达飞机。它们每个都包括一列，其中包含跑道标志。现在我要进行查询，将两个表合并在一起，计算有多少架飞机到达跑道，还有多少架飞机离开跑道。

这是我的尝试：

SELECT runway_sign as Landebahn, [Anzahl gelandet], [Anzahl gestartet]  from
    (
        SELECT runway_sign, COUNT(runway_sign) as [Anzahl gelandet], 0 as [Anzahl gestartet] FROM tbl_arriving_planes
            GROUP BY runway_sign
    ) as b
    UNION
    SELECT runway_sign as Landebahn, [Anzahl gelandet] ,[Anzahl gestartet]  from
    (
        SELECT runway_sign, 0 as [Anzahl gelandet], COUNT(runway_sign) as [Anzahl gestartet] FROM tbl_leaving_planes
            GROUP BY runway_sign
    ) as a

结果应如下所示：

runway_sign | number of arrived planes | number of leaving planes

Answer 1

您可以使用UNION ALL，然后再进行其他聚合：

SELECT runway_sign as Landebahn,
       SUM([Anzahl gelandet]),
       SUM([Anzahl gestartet])
FROM ((SELECT runway_sign, COUNT(runway_sign) as [Anzahl gelandet], 0 as [Anzahl gestartet]
       FROM tbl_arriving_planes
       GROUP BY runway_sign
      ) UNION ALL
      (SELECT runway_sign as Landebahn, 0 as [Anzahl gelandet], COUNT(runway_sign) as [Anzahl gestartet]
       FROM tbl_leaving_planes
       GROUP BY runway_sign
      )
     ) al
GROUP BY runway_sign;

另一种方法使用FULL JOIN而不是UNION ALL：

SELECT COALESCE(a.runway_sign, l.runway_sign) as Landebahn,
       a.[Anzahl gelandet],
       l.[Anzahl gestartet]
FROM (SELECT runway_sign, COUNT(runway_sign) as [Anzahl gelandet]
      FROM tbl_arriving_planes
      GROUP BY runway_sign
     ) a FULL JOIN
     (SELECT runway_sign as Landebahn, COUNT(runway_sign) as [Anzahl gestartet]
      FROM tbl_leaving_planes
      GROUP BY runway_sign
     ) l
     ON l.runway_sign = a.runway_sign

Answer 2

听起来您想对UNION的结果进行分组

SELECT runway_sign as Landebahn, SUM([Anzahl gelandet]) as [Anzahl gelandet], SUM([Anzahl gestartet]) as [Anzahl gestartet]
FROM (
    SELECT runway_sign, 1 as [Anzahl gelandet], 0 as [Anzahl gestartet] FROM tbl_arriving_planes
    UNION
    SELECT runway_sign, 0 as [Anzahl gelandet], 1 as [Anzahl gestartet] FROM tbl_leaving_planes
) as a
GROUP BY runway_sign

如何在查询中合并两个表？

2 个答案: