Home/ Questions/Q 3441098
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-18T08:30:40+00:00

Suppose I have a database which contains blog posts which have tags and I

  • 0

Suppose I have a database which contains blog posts which have tags and I want to retrieve a blog post with its tags.

I can do two queries:

SELECT title, text, date 
  FROM POSTS 
 WHERE id = 1

and

SELECT tag 
  FROM TAGS 
 WHERE post_id = 1

However I can also do it in a single query:

SELECT title, text, date, tag 
  FROM POSTS, TAGS 
 WHERE posts.id = 1 
  AND tags.post_id = posts.id

The latter is a bit wasteful, because it transfers the same title, text and date columns as many times as many tags the blog post have, but it may be faster, because there is only one trip to the server.

Is there some alternative for the latter query which avoids transferring duplicate data? Or is it not a big deal and I should use it anyway, because transferring a few hundred unused extra bytes is cheaper than making two separate queries?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    MySQL optimization isn’t quite as straightforward as this. You’ll find that sometimes multiple queries (possibly with a temp table in the middle) is much faster than a single query, especially with complex joins / aggregations going on. So, don’t assume that a single query will always be faster, because it won’t.

    However, a single query is often just as fast or faster than multiple queries, and it expresses what you’re doing much more succinctly. Don’t worry about a handful of bytes across the wire, they are trivial in comparison to everything else that’s going on.

    • 0