Join vs. sub-query

Question

I am an old-school MySQL user and have always preferred JOIN over sub-query. But nowadays everyone uses sub-query, and I hate it; I don\'t know why.

Answer 1

• A general rule is that joins are faster in most cases (99%).
• The more data tables have, the subqueries are slower.
• The less data tables have, the subqueries have equivalent speed as joins.
• The subqueries are simpler, easier to understand, and easier to read.
• Most of the web and app frameworks and their "ORM"s and "Active record"s generate queries with subqueries, because with subqueries are easier to split responsibility, maintain code, etc.
• For smaller web sites or apps subqueries are OK, but for larger web sites and apps you will often have to rewrite generated queries to join queries, especial if a query uses many subqueries in the query.

Some people say "some RDBMS can rewrite a subquery to a join or a join to a subquery when it thinks one is faster than the other.", but this statement applies to simple cases, surely not for complicated queries with subqueries which actually cause a problems in performance.