Question

我有两个查询得到：

最近的雪测量（1小时内）
24小时前测量。

当我UNION查询时，我希望这两个测量值位于不同的列中，但它们实际上是在单独的（重复的）行中返回的。见下面的输出。

SELECT snowfall.cms as now_snow, resorts.*, regions.name
FROM  snowfall
INNER JOIN resorts on resorts.id = snowfall.resort_id
INNER JOIN  regions ON resorts.region_id = regions.id
WHERE snowfall.timestamp >= SUBDATE( NOW( ) , INTERVAL 1 HOUR )
GROUP BY resorts.id
UNION
SELECT snowfall.cms as 24hr_snow, resorts.*, regions.name
FROM  snowfall
INNER JOIN resorts on resorts.id = snowfall.resort_id
INNER JOIN  regions ON resorts.region_id = regions.id
WHERE snowfall.timestamp >= SUBDATE( NOW() , INTERVAL 1 DAY)
GROUP BY resorts.id
ORDER BY now_snow DESC

我得到的结果是：

now_snow | resorts.name | ...
========================================
20       | The Mountain
15       | The Mountain
18       | The Hill
102      | The Hill

但是期待结果：

now_snow | 24hr_snow | resorts.name | ...
========================================
20       | 15        | The Mountain
18       | 102       | The Hill

在这种情况下，UNION是否正确？如何实现所需的输出？

Answer 1

UNION会在您的查询中添加行。为了扩大您的查询，您需要加入。

我建议在这种情况下自我加入。每天一次降雪，每小时降雪一次。两人都加入度假村id并按度假村名称分组。

SELECT sum(hourly.cms) as now_snow, sum(daily.cms) as 24hr_snow, resorts.name
FROM  
  snowfall daily
  INNER JOIN resorts on resorts.id = daily.resort_id
  INNER JOIN regions ON resorts.region_id = regions.id
  INNER JOIN snowfall hourly on resorts.id = hourly.resort_id
WHERE daily.timestamp >= SUBDATE( NOW() , INTERVAL 1 DAY)
  AND hourly.timestamp >= SUBDATE( NOW( ) , INTERVAL 1 HOUR )
GROUP BY resorts.name
ORDER BY now_snow DESC

你没有在你的帖子中使用聚合，mysql可能允许这样做，但为了清楚起见，我已经在这里添加了它。

返回MySQL Union Query的附加列值

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