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i) Between these two which one is more efficient:
Select A.* from A, B where A.b_id = B.id
or
Select A.* from A where A.b_id in (select id from B);
ii) How does Select A.* from A where A.b_id in (select id from B); really work? Is it internally translated into something like Select A.* from A, B where A.b_id = B.id or is (select id from B) evaluated for each row of A?
You can check this short article:
http://www.mysqlperformanceblog.com/2010/10/25/mysql-limitations-part-3-subqueries/