來自更多表的MySQL聯合/聯合結果

Question

我有一系列MySQL表，其中第一列是Unix時間格式化日期，第二列是每個表格具有不同格式的一些數據。

我使用類似這樣的一個組由月份的數據查詢：

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

我需要什麼樣的查詢，才能夠輸出所有這些「第二」列一行通過一年D組和月？ 即這樣每個返回的行包含「年，月，視圖，列2，列3」...

我試過使用UNION，但作爲「第二」列都是不同的，它返回一個每個表的行。即是這樣的：

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

你不得不這樣做如下：

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; 

由於每個選擇都包含相同的列，你就可以聚集在整個事情和選擇每行的最大值。顯然，如果數據是非數字或小於0，則必須替換不同的聚合函數。