Ben Huang's Blog

• subquery

SELECT FirstName, LastName, 
       OrderCount = (SELECT COUNT(O.Id) FROM [Order] O WHERE O.CustomerId = C.Id)
  FROM Customer C

• performing-a-query-on-a-result-from-another-query

SELECT COUNT(*), SUM(SUBQUERY.AGE) from
(
  SELECT availables.bookdate AS Date, DATEDIFF(now(),availables.updated_at) as Age
  FROM availables
  INNER JOIN rooms
  ON availables.room_id=rooms.id
  WHERE availables.bookdate BETWEEN '2009-06-25' AND date_add('2009-06-25', INTERVAL 4 DAY) AND rooms.hostel_id = 5094
  GROUP BY availables.bookdate
) AS SUBQUERY