LeetCode：Database 27.连续空余座位

Posted 2021-05-21 Xiao Miao

要求：几个朋友来到电影院的售票处，准备预约连续空余座位，你能利用表 cinema ，帮他们写一个查询语句，获取所有空余座位，并将它们按照 seat_id 排序后返回吗？

cinema表：

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

Result Table：

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

分析：
1.要求查询出连续的空位，所以需要查找的坐位首先是个空位，其次它的前一个坐位是空位，或者后一个坐位是空位即可满足要求

SQL语句：

#1.方法1
SELECT DISTINCT seat_id
FROM(
SELECT a.seat_id AS seat_id
FROM cinema a
JOIN cinema b
ON a.seat_id=b.seat_id-1
AND a.free=1 AND b.free=1

UNION ALL

SELECT b.seat_id AS seat_id
FROM cinema a
JOIN cinema b
ON a.seat_id=b.seat_id-1
AND a.free=1 AND b.free=1)c
ORDER BY seat_id ASC;
#2.方法2
SELECT seat_id FROM(
SELECT  seat_id,free,lead(free,1,0) over(ORDER BY seat_id) AS f1,lag(free,1,0) over() AS f2
FROM
cinema)a
WHERE free=1
AND (f1=1 OR f2=1)
ORDER BY seat_id ASC;