What types of indexes exist (B-tree, Hash)?

In PostgreSQL, there are several types of indexes, the main ones are:

• B-tree — the most common index type, used for fast equality and range searches. Suitable for most cases.
• Hash — an index for fast equality searches, but does not support range queries. Previously had limitations in PostgreSQL, now more stable.
• GIN (Generalized Inverted Index) — used for indexing arrays, JSONB, full-text search.
• GiST (Generalized Search Tree) — a flexible index for geometric data, full-text search, and other types.

Example of creating a B-tree index:

CREATE INDEX idx_users_email ON users USING btree(email);

The choice of index type depends on the nature of the queries and data.