mysql - SQL 组合跨多个表的两个选择

Question

所以我有这些表:

表 1:

facilities   emails
Fac 1        fac1@email.com
Fac 2        fac2@email.com
Fac 1 RE     fac1@email.com

表 2:

facilities  emails
fac1        fac1@email.com
fac2        fac3@email.com

现在，在这两个表上，我试图找出有多少设施正在使用每个地址电子邮件。我有两个 sql 查询可以做到这一点:

SELECT ce.email, count(*)  
AS TOTAL_FACILITIES 
FROM table1 
AS ce 
GROUP BY ce.email
ORDER BY TOTAL_FACILITIES DESC

SELECT ca.emails, count(*)  
AS TOTAL_FACILITIES 
FROM table2 
AS ca 
GROUP BY ca.emails
ORDER BY TOTAL_FACILITIES DESC

这为我提供了每张 table 的不同电子邮件以及有多少设施使用它们。我现在尝试使用连接将其合并为一个调用，但我似乎不知道如何使计数工作。

有什么建议吗？

Answer 1

您可能想要UNION它。

SELECT ce.email, count(*) AS TOTAL_FACILITIES 
FROM table1 AS ce 
GROUP BY ce.email
UNION
SELECT ca.emails, count(*) AS TOTAL_FACILITIES 
FROM table2 AS ca 
GROUP BY ca.emails
ORDER BY TOTAL_FACILITIES DESC

更好的解决方案是在聚合之前对其进行 UNION。

SELECT email, COUNT(*) AS TOTAL_FACILITIES
FROM (
    SELECT facilities, email
    FROM table1
    UNION ALL
    SELECT facilities, email
    FROM table2
)
GROUP BY email
ORDER BY TOTAL_FACILITIES DESC