mysql - 联合查询返回意外结果

Question

我组合了两个查询以获得我需要的结果，但它没有给出我想要的结果。

查询是这样的

SELECT COALESCE(SUM(rd.AMOUNT),0) as total from revenue_d AS rd JOIN  revenue_m AS rem on rd.RV_ID = rem.RV_ID Where MONTH(rd.SCROLL_DATE) = 5   and YEAR(rd.SCROLL_DATE)= 2016

Union 

SELECT COALESCE(SUM(rd.AMOUNT),0) as total from revenue_d AS rd JOIN revenue_m AS rem on rd.RV_ID = rem.RV_ID Where MONTH(rd.SCROLL_DATE) = 6 and YEAR(rd.SCROLL_DATE)= 2016;

它给我的结果是这样的

 +---------------+
 |     total     |
 +---------------+
 |       0       |
 +---------------+

虽然我想要这样

 +---------------+
 |     total     |
 +---------------+
 |       0       |
 +---------------+
 |       0       |
 +---------------+

甚至使用 Union ALL 但仍然得到相同的结果。

Answer 1

我认为总是执行最后一个查询，所以你应该这样写，

(first Query) UNION ALL (second query);

试试这个查询

(SELECT COALESCE(SUM(rd.AMOUNT),0) AS total 
    FROM revenue_d AS rd 
    JOIN  revenue_m AS rem ON rd.RV_ID = rem.RV_ID 
    WHERE MONTH(rd.SCROLL_DATE) = 5  AND YEAR(rd.SCROLL_DATE)= 2016)

  UNION ALL

(SELECT COALESCE(SUM(rd.AMOUNT),0) AS total 
    FROM revenue_d AS rd 
    JOIN revenue_m AS rem ON rd.RV_ID = rem.RV_ID 
    WHERE MONTH(rd.SCROLL_DATE) = 6 AND YEAR(rd.SCROLL_DATE)= 2016);