Question

Given the following tables:

 shows:

      title      | basic_ticket_price
 ----------------+--------------------
  Inception      |              $3.50
  Romeo & Juliet |              $2.00

performance:

  perf_date  | perf_time |     title
 ------------+-----------+----------------
  2012-08-14 | 00:08:00  | Inception
  2012-08-12 | 00:12:00  | Romeo & Juliet

booking:
  ticket_no | perf_date  | perf_time | row_no | person_id
 -----------+------------+-----------+--------+-----------
          1 | 2012-08-14 | 00:08:00  | P01    | 1
          2 | 2012-08-12 | 00:12:00  | O05    | 4
          3 | 2012-08-12 | 00:12:00  | A01    | 2

And an additional table: seat which contains a list of seats numbered like that of row_no in booking with an area name.

Having grouped the booked seats using this statement:

select count(row_no) AS row_no,
       area_name 
from seat 
where exists (select row_no 
              from   booking 
              where booking.row_no = seat.row_no) 
group by area_name;

which produces:

    row_no |  area_name
   --------+--------------
         1 | rear stalls
         2 | front stalls

How can I now use the counted rows and area_name to write a single SQL statement to produce a list showing the names of shows, dates and times of performances, and the number of booked seats in each area?

I’ve tried this:

 select s.title,
        perf_date,
        perf_time,
        count(row_no) AS row_no,
        area_name 
 from shows s, 
      performance,
      seat 
 where exists (select row_no 
               from booking 
               where booking.row_no =  seat.row_no) 
 group by area_name,s.title,performance.perf_date,performance.perf_time;

But it shows repeated rows:

      title      | perf_date  | perf_time | row_no |  area_name
 ----------------+------------+-----------+--------+--------------
  Romeo & Juliet | 2012-08-12 | 00:12:00  |      1 | rear stalls
  Romeo & Juliet | 2012-08-14 | 00:08:00  |      2 | front stalls
  Inception      | 2012-08-12 | 00:12:00  |      1 | rear stalls
  Inception      | 2012-08-14 | 00:08:00  |      2 | front stalls
  Inception      | 2012-08-14 | 00:08:00  |      1 | rear stalls
  Inception      | 2012-08-12 | 00:12:00  |      2 | front stalls
  Romeo & Juliet | 2012-08-14 | 00:08:00  |      1 | rear stalls
  Romeo & Juliet | 2012-08-12 | 00:12:00  |      2 | front stalls
  (8 rows)

Any help with solving this would be appreciated.

Answer 1

On a per performance entry, find all bookings. Of those bookings, link to the seats table to determine the area name. Then, simple COUNT(*) grouped by the criteria per show / area.

SELECT
      p.perf_date,
      p.perf_time,
      p.title,
      s.area_name,
      COUNT(*) as SeatsSold
   from
      performance p

         JOIN booking b
            ON p.perf_date = b.perf_date
            AND p.perf_time = b.perf_time

            JOIN seat s
               ON b.row_no = s.row_no
   group by
      p.perf_date,
      p.perf_time,
      p.title,
      s.area_name