如何對 SQL 中共享相同列名的 2 個單獨表中的值求和

Question

我有 2 個表，它們的列完全相同，但數據不同。 列是“姓名”、“性別”和“計數”。 第一個表名為 names_2014，第二個表名為 names_2015。 我的目標只是在這兩個表中找到前 5 個最受歡迎的名字。

我知道要獲得一張桌子最受歡迎的名字是：

SELECT name, count
FROM names_2014
ORDER BY count DESC 
LIMIT 5; 

但是，我最接近目標的是：

SELECT name, count
FROM names_2014
UNION DISTINCT  -- I've tried UNION ALL as well
SELECT name, SUM(count)
FROM names_2015
GROUP BY name
ORDER BY count DESC
LIMIT 5

我已經嘗試了許多類似的變體，但沒有一個是成功的。 似乎我需要合並兩個表，然后是 SUM(count) 和 GROUP BY 名稱，但我想我沒有正確合並表。 非常感謝任何幫助，因為我已經花了幾個小時在這上面，我覺得解決方案是如此接近，但我只是看不到它。 我是 SQL 的新手，只是想測試我的極限。

Answer 1

您可以對合並兩個表的子查詢執行聚合，如下所示：

select name, sum(count) cnt
from
(
  select name, count
  from names_2014
  union all
  select name, count
  from names_2015
 ) T
group by name
order by cnt desc
limit 5

Answer 2

從您的最終詢問中，不清楚您是否要按源表將這些前 5 名分開。 以下是您可能正在尋找的一個答案：

with name_2014 as (
select 'a' as name, 'm' as gender, 1 as cnt
union all 
select 'b' as name, 'f' as gender, 3 as cnt
union all 
select 'c' as name, 'm' as gender, 2 as cnt
),
name_2015 as (
select 'd' as name, 'f' as gender, 10 as cnt
union all 
select 'b' as name, 'f' as gender, 5 as cnt
union all 
select 'e' as name, 'm' as gender, 1 as cnt
)

(select 'name_2014' as src_table_name, name, sum(cnt) as total_counts from name_2014 group by name order by 3 desc limit 1)
union all  
(select 'name_2015' as src_table_name, name, sum(cnt) as total_counts from name_2015 group by name order by 3 desc limit 1)

此示例查詢將為您提供每個表的前 1 個名稱。 （您可以更改限制並從查詢中獲得前 5 名。）如果您不想知道表名，可以調整上述查詢。

如果您根本不關心源表而只想要前 5 名，那么：

with name_2014 as (
select 'a' as name, 'm' as gender, 1 as cnt
union all 
select 'b' as name, 'f' as gender, 3 as cnt
union all 
select 'c' as name, 'm' as gender, 2 as cnt
),
name_2015 as (
select 'd' as name, 'f' as gender, 10 as cnt
union all 
select 'b' as name, 'f' as gender, 5 as cnt
union all 
select 'e' as name, 'm' as gender, 1 as cnt
)

select name, sum(cnt) as total_count from 
(select name, cnt   from name_2014
union all  
select name, cnt   from name_2015)
group by 1 order by 2 desc limit 5