来自更多表的MySQL连接/联合结果

Question

我有一系列MySQL表，其中第一列是Unix时间格式的日期，第二列是一些数据，每个表具有不同的格式。

我正在使用与此查询类似的查询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

我需要哪种查询才能在按年和月分组的一行中输出所有这些“第二”列？ 即，使得返回的每一行都包含“年，月，视图，column2，column3” ...

我尝试使用UNION，但是由于“第二”列都不同，因此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，因此您可以汇总整个内容并为每行选择最大值。 显然，如果您的数据为非数字或小于0的数据，则必须替换为其他聚合函数。