将两个聚合查询合并到一个视图中

Question

我无法围绕此视图围绕我的大脑。我有两个疑问，我使用的定期报告：

mysql> select year(a.creation) as year, count(*) as 'built by year' 
    -> from hosts a 
    -> where year(a.creation) > 2013 
    -> group by year(a.creation); 
+------+---------------+ 
| year | built by year | 
+------+---------------+ 
| 2014 |   372 | 
| 2015 |   1115 | 
| 2016 |   779 | 
| 2017 |   268 | 
+------+---------------+ 
4 rows in set (0.00 sec) 

mysql> select year(b.decom) as year, count(*) as 'decomed by year' 
    -> from hosts b 
    -> where year(b.decom) > 2013 
    -> group by year(b.decom); 
+------+-----------------+ 
| year | decomed by year | 
+------+-----------------+ 
| 2015 |    68 | 
| 2016 |    816 | 
| 2017 |    27 | 
+------+-----------------+ 
3 rows in set (0.00 sec) 

我希望能够在一个单一的视图同时报告。

我已经尝试了几件事情，但最接近我已经在一个不错的笛卡尔连接结果。幸运的是，db是微小的：

mysql> select year(a.creation) as year, count(a.hostname) as 'built by year', count(b.hostname) as 'decomed by year' 
    -> from hosts a 
    -> left join hosts b on year(a.creation) = year(b.decom) 
    -> where year(a.creation) > 2013 group by year(a.creation), year(b.decom); 
+------+---------------+-----------------+ 
| year | built by year | decomed by year | 
+------+---------------+-----------------+ 
| 2014 |   372 |    0 | 
| 2015 |   75820 |   75820 | 
| 2016 |  635664 |   635664 | 
| 2017 |   7236 |   7236 | 
+------+---------------+-----------------+ 
4 rows in set (3.59 sec) 

Answer 1

你需要连接两个查询作为表像下面

selecgt a.year,a.built_by_year,b.decomed_by_year from(
        select year(a.creation) as year, count(*) as 'built_by_year' 
        from hosts a 
        where year(a.creation) > 2013 
        group by year(a.creation) 
       ) a 
      left join (
       select year(b.decom) as year, count(*) as 'decomed_by_year' 
       from hosts b 
       where year(b.decom) > 2013 
       group by year(b.decom) 
       ) b 
       on a.year=b.year 

Answer 2

...在评论看起来像废话:)

由于SQL查询再次，我想出的查询看起来像：

select * from 
(select year(a.creation) as year, count(*) as 'built by year' 
from hosts a 
where year(a.creation) > 2013 
group by year(a.creation) 
) x left join 
(select year(decom) as year, count(b.hostname) as 'decomed by year' 
from hosts b 
where year(b.decom) > 2013 
group by year(b.decom) 
) y 
on x.year = y.year