How to count and join two tables on mySQL from different database? - mysql

Question

I have two databases. Those are core and push.
This is subs table from core database:
+----+---------+----+----+-----+
| 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 |
+----+---------+----+----+-----+
and this is the buff table from push database:
+----+---------+-------+
| id | service | sub |
+----+---------+-------+
| 1 | DANG | daily |
| 2 | HOORAY | daily |
| 3 | DANG | daily |
+----+---------+-------+
i want to count subs and buff. i made this query for subs:
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 |
+---------+----+----+-----+
and this is the query for buff:
select service, count(1) as pushed
from buff a where sub = 'daily'
group by service;
RESULT:
+---------+---------+
| service | pushed |
+---------+---------+
| HOORAY | 1 |
| DANG | 2 |
+---------+---------+
So, my question is how to join those tables from two different databases?
here is the result that i expect:
+---------+----+----+-----+--------+
| 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 |
+---------+----+----+-----+--------+

Answer 1

One option is to join together your two current subqueries. I have used a full outer join below, because we want to handle the possibity that a service may appear in only the subs or buff table, but not both.
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

Answer 2

use database name as table name prefix with dot, I don't check the below sentence, it only show the idea:
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