How do INNER JOIN and EXISTS differ logically and in performance?

EXISTS is usually faster when the joined table is large, because MySQL stops after finding the first match.

INNER JOIN must process all matching rows, which can be slower in one-to-many relationships.

EXISTS uses indexes efficiently—the subquery often becomes an index lookup.

For small tables, the difference is minimal because MySQL may rewrite EXISTS and JOIN internally.

You need columns from both tables.

You expect 1-to-1 or 1-to-few relationships.

You want to aggregate data from the joined table.

You only need to check if related data exists.

You want to avoid row multiplication.

The joined table is large and indexed.

You need better performance in NOT EXISTS queries (faster than LEFT JOIN + IS NULL in many cases).