MySQL 连接/联合结果来自更多表

Question

我有一系列 MySQL 表，其中第一列是 Unix 时间格式的日期，第二列是每个表具有不同格式的一些数据。

我正在使用与此类似的查询来按月对数据进行分组:

SELECT YEAR(FROM_UNIXTIME(date)) AS year, MONTH(FROM_UNIXTIME(date)) AS month, SUM(views) AS views,
FROM stats
GROUP BY year, month

我需要什么样的查询才能在一行中输出按年和月分组的所有这些“第二”列？ 即每个返回的行都包含“年、月、 View 、column2、column3”...

我尝试使用 UNION，但是，由于“第二”列全部不同，它为每个表返回一行。即类似:

year1, month1, views, 0, 0...  
year1, month1, 0, column2, 0...  
year1, month1, 0, 0, column3...  
year2, month2, views, 0, 0...  
year2, month2, 0, column2, 0...  
year2, month2, 0, 0, column3...

Answer 1

您必须执行以下操作:

SELECT MAX(views) as views,
    MAX(column2) as column2,
    MAX(column3) as column3
FROM (
    SELECT YEAR(FROM_UNIXTIME(date)) AS year, 
        MONTH(FROM_UNIXTIME(date)) AS month, 
        SUM(views) AS views,
        0 AS column2,
        0 AS column3
    FROM stats
    GROUP BY year, month
    UNION
    SELECT YEAR(FROM_UNIXTIME(date)) AS year, 
        MONTH(FROM_UNIXTIME(date)) AS month, 
        0 AS views,
        sum(column2) AS column2,
        0 AS column3
    FROM stats
    GROUP BY year, month
    UNION
    SELECT YEAR(FROM_UNIXTIME(date)) AS year, 
        MONTH(FROM_UNIXTIME(date)) AS month, 
        0 AS views,
        0 AS column2,
        sum(column3) AS column3
    FROM stats
    GROUP BY year, month
)
GROUP BY year, month;

由于每个选择都包含相同的列，因此您将能够聚合整个内容并选择每行的最大值。显然，如果您的数据是非数字或小于 0，则必须替换不同的聚合函数。