JOINs usually faster. EXISTS often faster than IN. Correlated subqueries can be slow. Test with EXPLAIN. Modern optimizers may produce same plan.

JOINs typically faster than subqueries

EXISTS faster than IN for large datasets

Avoid correlated subqueries when possible

Index columns in both approaches

Test with real data volumes

Check execution plans

Always using JOINs without considering subqueries

Using IN instead of EXISTS with large datasets

Not testing performance differences

Sacrificing readability for minor performance gains

Not considering optimizer capabilities