如何减少规范化数据库中的查询数量？

Question

Imagine a table for articles. In addition to the main query:

SELECT * From articles WHERE article_id='$id'

We also need several other queries to get

SELECT * FROM users WHERE user_id='$author_id' // Taken from main query

SELECT tags.tag 
FROM tags 
  INNER JOIN tag_map 
    ON tags.tag_id=tag_map.tag_id 
WHERE article_id='$id'

and several more queries for categories, similar articles, etc

Question 1: Is it the best way to perform these queries separately with PHP and handle the given results, or there is way to combine them?

Question 2: In the absence of many-to-many relationships (e.g. one tag, category, author for every article identified by tag_id, category_id, author_id); What the best (fastest) was to retrieve data from the tables.

Answer 1

If all the relationships are one-many then you could quite easily retrieve all this data in one query such as

SELECT
    [fields required]
FROM
    articles a
    INNER JOIN
        users u ON a.author_id=u.user_id
    INNER JOIN 
        tag_map tm ON tm.article_id=a.article_id
    INNER JOIN
        tags t t.tag_id=tm.tag_id
WHERE
    a.article_id='$id'

This would usually be faster than the three queries separately along as your tables are indexed correctly as MySQL is built to do this! It would save on two round trips to the database and the associated overhead.