What experience do you have in using different types of indexes in databases in practice?

In my experience working with databases, I have used several types of indexes to optimize queries and improve performance:

• B-Tree indexes — the most common type, suitable for fast range searches and exact matches. For example, an index on a date or ID column.
• Hash indexes — effective for exact key lookups but do not support range queries. Used, for example, in some NoSQL databases.
• Full-text indexes — used for text search, allowing quick finding of words or phrases in large text fields.
• Expression or function-based indexes — allow indexing the result of computations, such as an index on LOWER(column) for case-insensitive searches.

Example of creating a B-Tree index in PostgreSQL:

CREATE INDEX idx_users_email ON users(email);

Using indexes significantly speeds up SELECT queries, but it is important to remember that they slow down INSERT/UPDATE/DELETE operations, so balancing their number and types is crucial.