拼多多大数据面试SQL-求连续段的起始位置和结束位置

数据仓库晨曦

修改于 2024-06-20 08:12:43

650

修改于 2024-06-20 08:12:43

一、题目

有一张表t_id记录了id，id不重复，但是会存在间断，求出连续段的起始位置和结束位置。

+-----+
| id  |
+-----+
| 1   |
| 2   |
| 3   |
| 5   |
| 6   |
| 8   |
| 10  |
| 12  |
| 13  |
| 14  |
| 15  |
+-----+

二、分析

本题对重新分组的考察，此类题目真的是常见呀！
使用累积求和方式对数据进行重新分组；
根据重新分组标签进行分组，使用聚合函数min(),max()计算出每组的起始位置和结束位置；

维度	评分
题目难度	⭐️⭐️⭐️⭐️
题目清晰度	⭐️⭐️⭐️⭐️⭐️
业务常见度	⭐️⭐️⭐️

三、SQL

1.lag()函数进行开窗计算与上一行的差值；

执行SQL

select id,
       id - lag(id) over (order by id) as diff
from t_id

查询结果

+-----+-------+
| id  | diff  |
+-----+-------+
| 1   | NULL  |
| 2   | 1     |
| 3   | 1     |
| 5   | 2     |
| 6   | 1     |
| 8   | 2     |
| 10  | 2     |
| 12  | 2     |
| 13  | 1     |
| 14  | 1     |
| 15  | 1     |
+-----+-------+

2.获得分组字段

根据diff进行判断，如果差值为1代表连续赋值为0，否则代表不连续赋值为1,然后使用sum()进行累积计算，获得分组依据字段。

执行SQL

select id,
       sum(if(diff = 1, 0, 1)) over (order by id) as group_type
from (select id,
             id - lag(id) over (order by id) as diff
      from t_id) t

查询结果

+-----+-------------+
| id  | group_type  |
+-----+-------------+
| 1   | 1           |
| 2   | 1           |
| 3   | 1           |
| 5   | 2           |
| 6   | 2           |
| 8   | 3           |
| 10  | 4           |
| 12  | 5           |
| 13  | 5           |
| 14  | 5           |
| 15  | 5           |
+-----+-------------+

3.得出结果

执行SQL

select group_type,
       min(id) as start_pos,
       max(id) as end_pos
from (select id,
             sum(if(diff = 1, 0, 1)) over (order by id) as group_type
      from (select id,
                   id - lag(id) over (order by id) as diff
            from t_id) t) tt
group by group_type

查询结果

+-------------+------------+----------+
| group_type  | start_pos  | end_pos  |
+-------------+------------+----------+
| 1           | 1          | 3        |
| 2           | 5          | 6        |
| 3           | 8          | 8        |
| 4           | 10         | 10       |
| 5           | 12         | 15       |
+-------------+------------+----------+

四、建表语句和数据插入

--建表语句
CREATE TABLE t_id (
id bigint COMMENT 'ID'
) COMMENT 'ID记录表'
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' 
;
-- 插入数据
insert into t_id(id)
values
(1),
(2),
(3),
(5),
(6),
(8),
(10),
(12),
(13),
(14),
(15)

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原始发表：2024-06-11，如有侵权请联系 cloudcommunity@tencent.com 删除

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