如何计算和连接mySQL上来自不同数据库的两个表？

我有两个数据库。它们是

core

和

push

这是

core

数据库中的

subs

表：

+----+---------+----+----+-----+
| id | service | ad | op | act |
+----+---------+----+----+-----+
| 1  | CHO     | 96 | x  |  1  |
| 2  | CHO     | 98 | x  |  1  |
| 3  | DANG    | 96 | x  |  1  |
| 4  | HOORAY  | 96 | x  |  1  |
| 5  | CHO     | 98 | x  |  1  |
| 6  | DANG    | 96 | x  |  1  |
+----+---------+----+----+-----+

+----+---------+-------+
| id | service |  sub  |
+----+---------+-------+
| 1  | DANG    | daily |
| 2  | HOORAY  | daily |
| 3  | DANG    | daily |
+----+---------+-------+

这是

push

数据库中的

buff

表：

+----+---------+----+----+-----+
| id | service | ad | op | act |
+----+---------+----+----+-----+
| 1  | CHO     | 96 | x  |  1  |
| 2  | CHO     | 98 | x  |  1  |
| 3  | DANG    | 96 | x  |  1  |
| 4  | HOORAY  | 96 | x  |  1  |
| 5  | CHO     | 98 | x  |  1  |
| 6  | DANG    | 96 | x  |  1  |
+----+---------+----+----+-----+

+----+---------+-------+
| id | service |  sub  |
+----+---------+-------+
| 1  | DANG    | daily |
| 2  | HOORAY  | daily |
| 3  | DANG    | daily |
+----+---------+-------+

我想数一数

subs

和

buff

。我对SUB进行了以下查询：

select service, ad, op, count(1) as sub where act=1 group by service,ad,op;

RESULT:
+---------+----+----+-----+
| service | ad | op | sub |
+---------+----+----+-----+
|  CHOO   | 96 | x  |  1  |
|  CHOO   | 98 | x  |  2  |
|  HOORAY | 96 | x  |  1  |
|  DANG   | 96 | x  |  2  |
+---------+----+----+-----+

这是对buff的查询：

select service, count(1) as pushed
from buff a where sub = 'daily'
group by service;

RESULT:
+---------+---------+
| service |  pushed |
+---------+---------+
|  HOORAY |    1    |
|  DANG   |    2    |
+---------+---------+

所以，我的问题是如何连接来自两个不同数据库的表？ 以下是我预期的结果：

 +---------+----+----+-----+--------+
 | service | ad | op | sub | pushed |
 +---------+----+----+-----+--------+
 |  CHOO   | 96 | x  |  1  |    0   |
 |  CHOO   | 98 | x  |  2  |    0   |
 |  HOORAY | 96 | x  |  1  |    1   |
 |  DANG   | 96 | x  |  2  |    2   |
 +---------+----+----+-----+--------+

---

一种选择是将当前的两个子查询连接在一起。我在下面使用了一个完整的外部联接，因为我们希望处理一个服务可能只出现在

subs

或

buff

表中，而不是同时出现在这两个表中

SELECT t1.service,
       t1.ad,
       t1.op,
       t1.sub,
       COALESCE(t2.pushed, 0) AS pushed
FROM
(
    SELECT service, ad, op, COUNT(*) AS sub
    FROM subs
    WHERE act = 1
    GROUP BY service,ad,op
) t1
LEFT JOIN
(
    SELECT service, COUNT(1) AS pushed
    FROM buff a
    WHERE sub = 'daily'
    GROUP BY service
) t2
    ON t1.service = t2.service
UNION
SELECT t2.service,
       COALESCE(t1.ad, -1),
       COALESCE(t1.op, -1),
       COALESCE(t1.sub, -1),
       t2.pushed
FROM
(
    SELECT service, ad, op, COUNT(*) AS sub
    FROM subs
    WHERE act = 1
    GROUP BY service,ad,op
) t1
RIGHT JOIN
(
    SELECT service, COUNT(1) AS pushed
    FROM buff a
    WHERE sub = 'daily'
    GROUP BY service
) t2
    ON t1.service = t2.service

---

一种选择是将当前的两个子查询连接在一起。我在下面使用了一个完整的外部联接，因为我们希望处理一个服务可能只出现在

subs

或

buff

表中，而不是同时出现在这两个表中

SELECT t1.service,
       t1.ad,
       t1.op,
       t1.sub,
       COALESCE(t2.pushed, 0) AS pushed
FROM
(
    SELECT service, ad, op, COUNT(*) AS sub
    FROM subs
    WHERE act = 1
    GROUP BY service,ad,op
) t1
LEFT JOIN
(
    SELECT service, COUNT(1) AS pushed
    FROM buff a
    WHERE sub = 'daily'
    GROUP BY service
) t2
    ON t1.service = t2.service
UNION
SELECT t2.service,
       COALESCE(t1.ad, -1),
       COALESCE(t1.op, -1),
       COALESCE(t1.sub, -1),
       t2.pushed
FROM
(
    SELECT service, ad, op, COUNT(*) AS sub
    FROM subs
    WHERE act = 1
    GROUP BY service,ad,op
) t1
RIGHT JOIN
(
    SELECT service, COUNT(1) AS pushed
    FROM buff a
    WHERE sub = 'daily'
    GROUP BY service
) t2
    ON t1.service = t2.service

---

使用数据库名作为带点的表名前缀，我不检查下面的句子，它只显示了想法：

 SELECT service, ad, op, count(1) AS sub FROM core.subs AS t1
 LEFT JOIN push.buff AS t2 ON t1.service=t2.service WHERE t1.act=1
 AND sub = 'daily' GROUP BY t1.service,t1.ad,t1.op

---

使用数据库名作为带点的表名前缀，我不检查下面的句子，它只显示了想法：

 SELECT service, ad, op, count(1) AS sub FROM core.subs AS t1
 LEFT JOIN push.buff AS t2 ON t1.service=t2.service WHERE t1.act=1
 AND sub = 'daily' GROUP BY t1.service,t1.ad,t1.op

---

它起作用了。非常感谢你的帮助。上帝保佑你：）@arifinistighfarizahro为真正丑陋的外部连接而作的演讲。如果您确信这两个表中的一个表保证所有服务都存在于另一个表中，那么您只需使用

联合的一半就可以了。非常感谢你的帮助。上帝保佑你：）@arifinistighfarizahro为真正丑陋的外部连接而作的演讲。如果您确信两个表中的一个表保证所有服务都存在于另一个表中，那么您只需使用
联合的一半即可。