Ordering a parent table by SUM() of colums of two of its child tables
SELECT s.name as storename, i.turnover + r.turnover as turnover
FROM companies c
INNER JOIN stores s on s.company_id = c.id
INNER JOIN ( SELECT store_id, SUM(total) as turnover
             FROM invoices
             WHERE QUARTER(date_time) = 4
               AND YEAR(date_time) = 2019
             GROUP BY store_id ) i ON i.store_id = s.id 
INNER JOIN ( SELECT store_id, SUM(total) as turnover
             FROM receipts
             WHERE QUARTER(date_time) = 4
               AND YEAR(date_time) = 2019
             GROUP BY store_id ) r ON r.store_id = s.id 
WHERE c.name = 'Com1' 
ORDER BY turnover DESC


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