Understanding Compound Indexes in PostgreSQL and Ruby on Rails

In database optimization, compound indexes (also called composite indexes) play a significant role in enhancing query performance, especially in applications that filter or sort by multiple columns. In this article, we’ll explore how compound indexes work in PostgreSQL, how to implement them in Ruby on Rails, and when to use them for the best performance.

What is a Compound Index?

A compound index in PostgreSQL is an index that covers more than one column in a table. Compound indexes can optimize the performance of queries that involve these columns, enabling efficient lookups, filtering, and sorting based on the indexed fields.

How Compound Indexes Work in PostgreSQL

In PostgreSQL, a compound index allows you to specify an index over multiple columns, which can be beneficial for queries involving those columns in the same order defined in the index.

Key Points to Understand:

Order Matters: The order of columns in a compound index matters because PostgreSQL reads them left to right. For example, an index on (column_a, column_b) can efficiently serve a query filtering by column_a alone or by both column_a and column_b together, but it may not help with…