Convert SQL WHERE IN to JOIN

Question

I have a database storing various information about fictional people. There is a table person with general information, such as name, adress etc and some more specific table

Answer 1

Depends on your SQL engine. Newer SQL systems that have reasonable query optimizers will most likely rewrite both IN and JOIN queries to the same plan. Typically, a sub-query (IN Clause) is rewritten using a join.

In simple SQL engines that may not have great query optimizers, the join should be faster because they may run sub-queries into a temporary in-memory table before running the outer query.

In some SQL engines that have limited memory footprint, however, the sub-query may be faster because it doesn't require joining -- which produces more data.