What is a composite index?

A composite index is an index in a database that is created on multiple columns (fields) of a table simultaneously. It helps to speed up queries that filter or sort data based on a combination of these fields.

For example, if you have a table with fields user_id and created_at, and you frequently run queries with conditions on both fields, creating a composite index on (user_id, created_at) will allow the database to find the required records faster.

In Go, when working with databases, composite indexes are created at the DBMS level (for example, in PostgreSQL or MySQL), and in code, you simply use the corresponding queries. It is important to design composite indexes correctly, considering the order of fields, as the index is most effective for queries starting with the first field of the index.

Example SQL for creating a composite index:

CREATE INDEX idx_user_created ON orders (user_id, created_at);