SQL面试题练习 —— 无效搜索

1 题目

现有一份用户搜索日志，包含用户ID，时间，用户搜索内容。定义无效搜索：如果用户下一次搜索内容中包含本次搜索内容，则认为本次搜索为无效搜索。请查询用户无效搜索记录。

样例数据

+---------+---------------------+------------------------+
| user_id |     search_time      |     search_content      |
+---------+---------------------+------------------------+
|       1 | 2022-01-01 10:00:00 |          apple           |
|       1 | 2022-01-01 11:30:00 |    banana and apple      |
|       1 | 2022-01-01 12:45:00 |        fruit salad       |
|       1 | 2022-01-01 15:00:00 |         apple pie        |
|       1 | 2022-01-01 16:20:00 |   applesauce recipe      |
|       2 | 2022-01-01 10:00:00 |        cat food          |
|       2 | 2022-01-01 11:30:00 |   wet vs dry cat food    |
|       2 | 2022-01-01 12:45:00 | homemade cat food recipe |
|       2 | 2022-01-01 14:00:00 | cat food brands to avoid |
|       2 | 2022-01-01 16:20:00 | best cat food for i...   |
|       3 | 2022-01-01 10:00:00 |          book            |
|       3 | 2022-01-01 11:30:00 |  books like Harry Potter|
|       3 | 2022-01-01 13:00:00 |best selling books ...   |
|       3 | 2022-01-01 14:30:00 |   bookstores near me    |
|       3 | 2022-01-01 15:45:00 |    how to publish a book|
+---------+---------------------+------------------------+

2 建表语句

--建表语句
CREATE TABLE user_search_log (user_id STRING,search_time TIMESTAMP,search_content STRING
) STORED AS PARQUET;
--插入数据
INSERT INTO user_search_log
VALUES('1', '2022-01-01 10:00:00', 'apple'),('1', '2022-01-01 11:30:00', 'banana and apple'),('1', '2022-01-01 12:45:00', 'fruit salad'),('1', '2022-01-01 15:00:00', 'apple pie'),('1', '2022-01-01 16:20:00', 'applesauce recipe'),('2', '2022-01-01 10:00:00', 'cat food'),('2', '2022-01-01 11:30:00', 'wet vs dry cat food'),('2', '2022-01-01 12:45:00', 'homemade cat food recipe'),('2', '2022-01-01 14:00:00', 'cat food brands to avoid'),('2', '2022-01-01 16:20:00', 'best cat food for indoor cats'),('3', '2022-01-01 10:00:00', 'book'),('3', '2022-01-01 11:30:00', 'books like Harry Potter'),('3', '2022-01-01 13:00:00', 'best selling books of all time'),('3', '2022-01-01 14:30:00', 'bookstores near me'),('3', '2022-01-01 15:45:00', 'how to publish a book');

3 题解

（1）查询出下一行数据，并把下一行搜索内容作为新字段放到本行

select user_id,search_time,search_content,lead(search_content) over (partition by user_id order by search_time asc) as next_search_content
from user_search_log

执行结果

+----------+------------------------+---------------------------------+---------------------------------+
| user_id  |      search_time       |         search_content          |       next_search_content       |
+----------+------------------------+---------------------------------+---------------------------------+
| 1        | 2022-01-01 10:00:00.0  | apple                           | banana and apple                |
| 1        | 2022-01-01 11:30:00.0  | banana and apple                | fruit salad                     |
| 1        | 2022-01-01 12:45:00.0  | fruit salad                     | apple pie                       |
| 1        | 2022-01-01 15:00:00.0  | apple pie                       | applesauce recipe               |
| 1        | 2022-01-01 16:20:00.0  | applesauce recipe               | NULL                            |
| 2        | 2022-01-01 10:00:00.0  | cat food                        | wet vs dry cat food             |
| 2        | 2022-01-01 11:30:00.0  | wet vs dry cat food             | homemade cat food recipe        |
| 2        | 2022-01-01 12:45:00.0  | homemade cat food recipe        | cat food brands to avoid        |
| 2        | 2022-01-01 14:00:00.0  | cat food brands to avoid        | best cat food for indoor cats   |
| 2        | 2022-01-01 16:20:00.0  | best cat food for indoor cats   | NULL                            |
| 3        | 2022-01-01 10:00:00.0  | book                            | books like Harry Potter         |
| 3        | 2022-01-01 11:30:00.0  | books like Harry Potter         | best selling books of all time  |
| 3        | 2022-01-01 13:00:00.0  | best selling books of all time  | bookstores near me              |
| 3        | 2022-01-01 14:30:00.0  | bookstores near me              | how to publish a book           |
| 3        | 2022-01-01 15:45:00.0  | how to publish a book           | NULL                            |
+----------+------------------------+---------------------------------+---------------------------------+

在 MySQL 中，INSTR 函数的语法如下：INSTR(string, substring)，string 是要搜索的字符串。
substring 是要查找的子字符串。INSTR 函数返回子字符串在字符串中首次出现的位置（从 1 开始）。如果未找到子字符串，则返回 0。

（2）比较搜索内容是否为下一次搜索内容的子字符串，给判断逻辑打标记（如果是返回1，否则返回0）

select user_id,search_time,search_content,lead(search_content) over (partition by user_id order by search_time asc)                                      as next_search_content,If(instr(lead(search_content) over (partition by user_id order by search_time asc), search_content) > 0, 1,0)                                                                                                          as flag
from user_search_log

执行结果

+----------+------------------------+---------------------------------+---------------------------------+-------+
| user_id  |      search_time       |         search_content          |       next_search_content       | flag  |
+----------+------------------------+---------------------------------+---------------------------------+-------+
| 1        | 2022-01-01 10:00:00.0  | apple                           | banana and apple                | 1     |
| 1        | 2022-01-01 11:30:00.0  | banana and apple                | fruit salad                     | 0     |
| 1        | 2022-01-01 12:45:00.0  | fruit salad                     | apple pie                       | 0     |
| 1        | 2022-01-01 15:00:00.0  | apple pie                       | applesauce recipe               | 0     |
| 1        | 2022-01-01 16:20:00.0  | applesauce recipe               | NULL                            | 0     |
| 2        | 2022-01-01 10:00:00.0  | cat food                        | wet vs dry cat food             | 1     |
| 2        | 2022-01-01 11:30:00.0  | wet vs dry cat food             | homemade cat food recipe        | 0     |
| 2        | 2022-01-01 12:45:00.0  | homemade cat food recipe        | cat food brands to avoid        | 0     |
| 2        | 2022-01-01 14:00:00.0  | cat food brands to avoid        | best cat food for indoor cats   | 0     |
| 2        | 2022-01-01 16:20:00.0  | best cat food for indoor cats   | NULL                            | 0     |
| 3        | 2022-01-01 10:00:00.0  | book                            | books like Harry Potter         | 1     |
| 3        | 2022-01-01 11:30:00.0  | books like Harry Potter         | best selling books of all time  | 0     |
| 3        | 2022-01-01 13:00:00.0  | best selling books of all time  | bookstores near me              | 0     |
| 3        | 2022-01-01 14:30:00.0  | bookstores near me              | how to publish a book           | 0     |
| 3        | 2022-01-01 15:45:00.0  | how to publish a book           | NULL                            | 0     |
+----------+------------------------+---------------------------------+---------------------------------+-------+

（3）限制标签为1，查询出最后结果

select user_id,search_time,search_content
from (select user_id,search_time,search_content,if(instr(lead(search_content) over (partition by user_id order by search_time asc), search_content) > 0, 1,0) as flagfrom user_search_log) t
where flag = 1;

执行结果

+----------+------------------------+-----------------+
| user_id  |      search_time       | search_content  |
+----------+------------------------+-----------------+
| 1        | 2022-01-01 10:00:00.0  | apple           |
| 2        | 2022-01-01 10:00:00.0  | cat food        |
| 3        | 2022-01-01 10:00:00.0  | book            |
+----------+------------------------+-----------------+

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