Can you explain how composite indexes work in data storage systems?

A composite index is an index created on multiple columns of a table simultaneously. It helps to speed up data retrieval and sorting when queries filter or sort by several fields.

How it works:

• The index stores values of multiple columns in a specific order.
• When searching by multiple fields, the database can use this index to quickly find the needed records without scanning the entire table.
• The order of columns in the index affects which queries will efficiently use the index.

For example, if there is an index on (A, B), then queries filtering by A or by A and B will use the index, but queries only on B will not.

This helps optimize queries that frequently filter or sort data by multiple fields simultaneously.