Problem

Several friends at a cinema ticket office would like to reserve consecutive available seats. Can you help to query all the consecutive available seats order by the seat_id using the following cinema table?

Table: Cinema

1
2
3
4
5
6
7

| seat_id | free |
|---------|------|
| 1       | 1    |
| 2       | 0    |
| 3       | 1    |
| 4       | 1    |
| 5       | 1    |

Your query should return the following result for the sample case above.

1
2
3
4
5

| seat_id |
|---------|
| 3       |
| 4       |
| 5       |

Note:

  • The seat_id is an auto increment int, and free is bool (‘1’ means free, and ‘0’ means occupied.).
  • Consecutive available seats are more than 2(inclusive) seats consecutively available.

Solution

Method 1 - using where clause

Code

1
2
3
4
5
6

select c1.seat_id
from cinema c1, cinema c2
where ((c1.seat_id = c2.seat_id+1) or
       (c1.seat_id = c2.seat_id-1)) and 
    (c1.free = 1) and (c2.free = 1)
group by c1.seat_id