Join query or subquery

Question

Are there rules of thumb for developers when to use join instead of subquery or are they the same.

Answer 1

In SQL Server a correlated subquery usually performs worse than a join or, often even better for performance, a join to a derived table. I almost never write a subquery for anything that will have to be performed multiple times. This is because correlated subqueries often basically turn your query into a cursor and run one row at a time. In databases it is usually better to do things in a set-based fashion

Answer 2

Theoretically every subquery can be changed to a join query.