MyISAM 性能：加入分解？
在 高性能 MySQL 第 159 页，他们讨论了将复杂查询分解为简单查询：
转换
SELECT * FROM tag
JOIN tag_post ON tag_post.tag_id=tag.id
JOIN post ON tag_post.post_id=post.id
WHERE tag.tag='mysql';
为
SELECT * FROM tag WHERE tag='mysql';
SELECT * FROM tag_post WHERE tag_id=1234;
SELECT * FROM post WHERE post.id in (123,456,567,9098,8904);
并在应用程序中自行进行实际连接。
我的问题是，当最终查询有一个 where 子句需要匹配几千个 ID（实际表本身有大约 500k 条目）时，这是否仍然是一个好主意。
我的意思是，使用类似的查询
SELECT * FROM post WHERE post.id in (123,456,567, ... <a few thousand IDs here> ... ,9098,8904);
而不是上面的连接语句会受到很大的惩罚吗？将此逻辑移至数据库内的存储过程是否有帮助（同时考虑 MySQL 中存储过程的实现有多差）？
in High Performance MySQL on page 159 they talk about breaking up complex queries into simple ones:
Converting
SELECT * FROM tag
JOIN tag_post ON tag_post.tag_id=tag.id
JOIN post ON tag_post.post_id=post.id
WHERE tag.tag='mysql';
To
SELECT * FROM tag WHERE tag='mysql';
SELECT * FROM tag_post WHERE tag_id=1234;
SELECT * FROM post WHERE post.id in (123,456,567,9098,8904);
And sort of doing the actual join yourself in your application.
My Question is wether this is stil such a good idea when the final query has a where-clause with a few thousand IDs it needs to match (the actual table itself has about 500k entries).
What I mean is, will there be a big penalty for having a query like
SELECT * FROM post WHERE post.id in (123,456,567, ... <a few thousand IDs here> ... ,9098,8904);
instead of the join-statement above? Would it help to move this logic to Stored Procedures inside the Database (while considering how poorly stored procedures are implemented in MySQL)?
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连接分解在某些情况下很有用，但在大多数情况下连接会更快。
在你的例子中，我会坚持使用连接，而不是在 IN 子句中传递几千个 ID。
Join decomposition is useful in certain situations, but in most situations the joins are going to be faster.
In your case, I would stick with the joins instead of passing in a few thousand IDs in an IN clause.