Can I sum the count of two columns from two different tables? - sql

Question

I'm trying to add together the counts of two different tables and group them by the same variable
Here is what I have so far:
SELECT a.storenumber,
Count (howmanytotal) AS total_counts_store
FROM (
SELECT month_counts.howmany,
new_counts.howmany) AS howmanytotal
from (
SELECT a.storenumber,
count (b.riid_) AS howmany
FROM $b$ b
INNER JOIN $a$ a
ON b.riid_=a.riid_
GROUP BY a.storenumber) month_counts
FROM (
SELECT a.storenumber,
count (c.riid_) AS howmany
FROM $c$ c
INNER JOIN $a$ a
ON c.riid_=a.riid_
GROUP BY a.storenumber) new_counts
ON month_counts.storenumber = new_counts.storenumber) theend
where I'm at now:
SELECT howmanytotal AS total_counts_store
FROM (
SELECT Count (howmany) AS howmanytotal)
FROM (
SELECT month_counts.howmany,
new_counts.howmany)
FROM (
SELECT a.storenumber,
count (b.riid_) AS howmany
FROM $b$ b
inner join $a$ a
ON b.riid_=a.riid_
GROUP BY a.storenumber) month_counts
UNION
(
SELECT count (c.riid_) AS howmany
FROM $c$ c
inner join $a$ a
ON c.riid_=a.riid_
GROUP BY a.storenumber) new_counts
ON month_counts.storenumber = new_counts.storenumber) ORDER BY $a$.storenumber
Getting this error: Error: java.sql.SQLSyntaxErrorException: ORA-00923: FROM keyword not found where expected
Please correct SELECT statement:

Answer 1

Join the subqueries:
select
storenumber,
month_counts.howmany as month_count,
new_counts.howmany as new_count,
month_counts.howmany + new_counts.howmany as total_count
from (...) month_counts
join (...) new_counts using (storenumber)
order by storenumber;
If it is possible for a storenumber to be missing from one of the subquery results, then outer join and use COALESCE or NVL to deal with the nulls. Here is a query with a full outer join, which is not available in MySQL, but in Oracle and many other DBMS.
select
storenumber,
month_counts.howmany as month_count,
new_counts.howmany as new_count,
nvl(month_counts.howmany, 0) + nvl(new_counts.howmany, 0) as total_count
from (...) month_counts
full outer join (...) new_counts using (storenumber)
order by storenumber;

Answer 2

Ending up using sum and union to complete. Thank you for your help.
SELECT storenumber,
SUM(howmany) AS howmanytotal
FROM (SELECT a.storenumber,
Count (b.riid_) AS howmany
FROM $b$ b
inner join $a$ a
ON b.riid_ = a.riid_
GROUP BY a.storenumber
UNION
SELECT a.storenumber,
Count (c.riid_) AS howmany
FROM $c$ c
inner join $a$ a
ON c.riid_ = a.riid_
GROUP BY a.storenumber)
GROUP BY storenumber
ORDER BY storenumber
This gave me a list of store ids and how many active subscribers we have at each store (taken from two separate tables)