Many queries can use either subqueries or JOINs. Each has advantages. JOINs often faster but subqueries sometimes clearer. Test both approaches.

JOINs typically faster for combining data. Subqueries clearer for existence checks (EXISTS). Correlated subqueries can be slow. Modern optimizers often convert between them.

Senior developers must know when to use subqueries vs JOINs. This knowledge is critical for code reviews and performance tuning.

Same query can be written with JOIN or subquery. Choice affects performance and readability. Understanding trade-offs is essential for query optimization.