Question

I have got two tables:

Event
+----------+---------+--------------+
| event_id | name    | date         |
+----------+------+-----------------+
| 1        | Event 1 | 26/03/2012   |
+----------+------+-----------------+
| 2        | Event 2 | 27/03/2012   |
+----------+------+-----------------+

Reservation
+----------------+------------+--------------+
| reservation_id | date       | themed_id    |
+----------------+------------+--------------+
| 1              | 26/03/2012 | 1            |
+----------------+------------+--------------+
| 2              | 26/03/2012 | 1            |
+----------------+------------+--------------+
| 3              | 27/03/2012 | 2            |
+----------------+------------+--------------+
| 4              | 26/03/2012 | 1            |
+----------------+------------+--------------+

How will I display all the events which appear less than 3 times in the reservation table.

The output will be:

+----------+---------+--------------+
| event_id | name    | date         |
+----------+------+-----------------+
| 2        | Event 2 | 27/03/2012   |
+----------+------+-----------------+

As event two has only appeared once in reservation

thanks

Answer 1

SELECT *
FROM Event
WHERE event_id IN (
SELECT themed_id
FROM Reservation
GROUP BY themed_id
HAVING COUNT(*) < 3)

I have not tested but the base idea is this.