力扣sql中等篇练习(三)
1 树节点
1.1 题目内容
1.1.1 基本题目信息
1.1.2 示例输入输出
1.2 示例sql语句
SELECT id,case when p_id is null then 'Root'when (id not in (SELECT distinct p_id FROM tree WHERE p_id is not null))=1 then 'Leaf'else 'Inner'end type
FROM tree
1.3 运行截图
2 两人之间的通话次数
2.1 题目内容
2.1.1 基本题目信息
2.1.2 示例输入输出
2.2 示例sql语句
SELECT from_id person1,to_id person2,count(*) call_count,sum(duration) total_duration
FROM Calls
GROUP BY least(from_id,to_id),greatest(from_id,to_id)
2.3 运行截图
3 换座位
3.1 题目内容
3.1.1 基本题目信息
3.1.2 示例输入输出
3.2 示例sql语句
SELECT IF(id%2=0,id-1,IF(id=(SELECT count(*) FROM Seat),id,id+1)) id,student
FROM Seat
ORDER BY id asc
3.3 运行截图