SQL

SQL management 2009-2014

The following query is executing very slowly on a large amount of data.

Would an Index help to speed it up? If so, which columns should be indexed? Explain why an index can help but doesn't always.

SELECT c.cinema_name, s.price*SUM(t.ticket_id) AS 'total' FROM Cinema c INNER JOIN MovieSession s ON c.cinema_id = s.cinema_id INNER JOIN Ticket t ON t.ticket_id = s.ticket_id GROUP BY s.price, c.cinema_name HAVING SUM(t.ticket_id) > 5