Among the listed query types (SELECT, INSERT, UPDATE, DELETE), which ones speed up indexes and which ones slow them down?

Indexes in a database speed up read operations, such as SELECT queries, because they allow quick access to the needed records without scanning the entire table.

However, for write operations (INSERT, UPDATE, DELETE), indexes can slow down performance because updating data also requires updating the corresponding index structures.

Thus:

• SELECT — are accelerated by indexes.
• INSERT, UPDATE, DELETE — may be slowed down due to the need to keep indexes up to date.