根据时间变量对两个表中的一对 COUNT 求和

花了一个多小时的时间寻找这个问题的答案，但运气不佳。我有两个具有相同列名的区域表，我可以根据以下查询为任一表提供结果列表（将 Table2 替换为 Table1）：

SELECT Table1.YEAR, FORMAT(COUNT(Table1.id),0) AS Total
FROM Table1
WHERE Table1.variable='Y' 
GROUP BY Table1.YEAR

理想情况下，我希望得到一个结果，该结果可以按年份提供计数总和，因此不要：

|     REGION 1     |     |     REGION 2     |
|  YEAR  |  Total  |     |  YEAR  |  Total  |
|  2010  |    5    |     |  2010  |    1    |
|  2009  |    2    |     |  2009  |    3    |
|        |         |     |  2008  |    4    |

我会有：

|     MERGED       |
|  YEAR  |  Total  |
|  2010  |    6    |
|  2009  |    5    |
|  2008  |    4    |

我尝试过各种 JOIN 和其他想法，但我认为我陷入了 SUM 和 COUNT 问题。任何帮助将不胜感激，谢谢！

SELECT `YEAR`, FORMAT(SUM(`count`), 0) AS `Total`
FROM (
    SELECT `Table1`.`YEAR`, COUNT(*) AS `count`
    WHERE `Table1`.`variable` = 'Y'
    GROUP BY `Table1`.`YEAR`
    UNION ALL
    SELECT `Table2`.`YEAR`, COUNT(*) AS `count`
    WHERE `Table2`.`variable` = 'Y'
    GROUP BY `Table2`.`YEAR`
) AS `union`
GROUP BY `YEAR`