Leetcode SQL: 1148. Article Views

1148. Article Views I

Corrected SQL Code:

SELECT DISTINCT [author_id] AS id
FROM Views WITH (NOLOCK)
WHERE author_id = viewer_id
ORDER BY [author_id];

Explanation:

SELECT DISTINCT [author_id] AS id:
We are selecting the author_id column from the Views table, but we are using the DISTINCT keyword to ensure that only unique author_ids are returned. The AS id renames the column to id in the result set.
- DISTINCT ensures that if the same author views their own article multiple times, only one entry is returned for that author.
- AS id renames the author_id column to id for simplicity.
我们从 Views 表中选择 author_id 列，并使用 DISTINCT 关键字确保只返回唯一的 author_id。AS id 将列重命名为 id。
- DISTINCT 确保如果同一个作者多次查看自己的文章，结果集中只返回该作者的一条记录。
- AS id 将 author_id 列重命名为 id，使结果更加简洁。
FROM Views WITH (NOLOCK):
The FROM clause specifies the Views table as the source of data. The WITH (NOLOCK) hint is used to allow the query to read data without locking the table, which can improve performance in high-concurrency environments. However, using NOLOCK can result in reading uncommitted or dirty data.

FROM 子句指定 Views 表为数据源。WITH (NOLOCK) 提示允许查询在不锁定表的情况下读取数据，这可以提高高并发环境下的性能。然而，使用 NOLOCK 可能会导致读取未提交或脏数据。
WHERE author_id = viewer_id:
The WHERE clause filters the rows to only include cases where the author_id is equal to the viewer_id, meaning the author is viewing their own article.

WHERE 子句筛选出 author_id 等于 viewer_id 的行，即作者查看自己文章的情况。
ORDER BY [author_id]:
The ORDER BY clause ensures that the result set is sorted by author_id. This provides an ordered list of authors who viewed their own articles.

ORDER BY 子句确保结果集按 author_id 排序。这提供了一个按顺序列出的查看自己文章的作者列表。

Key Concepts:

DISTINCT:
The DISTINCT keyword removes duplicate entries. This is crucial in this case because an author could view their own article multiple times. Without DISTINCT, the query would return multiple rows for the same author_id if they viewed their article more than once.

DISTINCT:
DISTINCT 关键字删除重复的条目。这在此处至关重要，因为作者可能多次查看自己的文章。如果没有 DISTINCT，查询会为同一作者返回多行记录。
NOLOCK:
The WITH (NOLOCK) hint allows the query to avoid locking the table during reads, improving performance. However, it may lead to reading uncommitted or dirty data, which could cause inconsistent results.

NOLOCK:
WITH (NOLOCK) 提示允许查询在读取时不锁定表，从而提高性能。然而，它可能导致读取未提交或脏数据，可能导致结果不一致。
ORDER BY:
Sorting the result by author_id ensures the result is returned in a consistent and meaningful order.

ORDER BY:
按 author_id 排序确保结果按顺序返回，提供一致且有意义的顺序。

Warnings:

Reading Dirty Data:
When using WITH (NOLOCK), be cautious because it may read uncommitted or dirty data. This is acceptable in environments where performance is prioritized over data accuracy, but be aware of potential inconsistencies.

读取脏数据:
使用 WITH (NOLOCK) 时要谨慎，因为它可能会读取未提交的脏数据。这在性能优先于数据准确性的环境中是可以接受的，但要注意潜在的不一致性。

Summary:

This query retrieves a list of unique author_ids where the authors have viewed their own articles. The DISTINCT keyword ensures only unique entries are returned, and the result is sorted by author_id. The WITH (NOLOCK) hint is used to improve performance by avoiding table locks, but be cautious of potential dirty data reads.

中文总结:
该查询检索了唯一的 author_id 列表，表示作者查看了自己撰写的文章。DISTINCT 确保只返回唯一的条目，结果按 author_id 排序。WITH (NOLOCK) 提示用于提高性能，避免锁表，但需要注意潜在的脏数据读取问题。

Tips:

Indexing:
Consider creating an index on the author_id and viewer_id columns to improve query performance, especially if the Views table is large.

索引:
考虑在 author_id 和 viewer_id 列上创建索引，以提高查询性能，尤其是在 Views 表很大的情况下。
When to Avoid NOLOCK:
If you need accurate and consistent data, avoid using NOLOCK, especially in environments where data integrity is critical (e.g., financial systems).

何时避免使用 NOLOCK:
如果需要准确和一致的数据，避免使用 NOLOCK，特别是在数据完整性至关重要的环境中（如金融系统）。

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