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PostgreSQL: Creating and Using Partial Indexes

Optimize queries with partial indexes in PostgreSQL. This guide explains how to create indexes on subsets of data based on specific conditions.

Creating and Using Partial Indexes in PostgreSQL

PostgreSQL partial indexes are indexes created on a subset of a table's rows, based on a specified condition. They improve query performance by reducing the index size and the amount of data the database needs to examine when running a query.

Understanding Partial Indexes

A regular index covers all rows in a table. A partial index, however, only covers rows that meet a particular condition. This is especially useful when you have queries that frequently filter data based on a specific condition. By limiting the index to only the relevant rows, you reduce index size and improve query performance.

Creating a Partial Index

The syntax for creating a partial index is:


CREATE INDEX index_name ON table_name (column_list) WHERE condition;

The `WHERE` clause specifies the condition that determines which rows are included in the index. Only rows satisfying this condition will be indexed.

Example: Indexing Inactive Buyers

(Note: This example assumes you have a `Buyer` table. Screenshots from the original text are not included here. Please refer to the original document for visual confirmation of the commands' success. The descriptions below aim to convey the information in those screenshots.)

  1. Create Table: Create a `Buyer` table with columns including an `active` column (0 for inactive, 1 for active).
  2. Insert Data: Insert sample data into the `Buyer` table.
  3. Query Without Index: Select inactive buyers (`WHERE active = 0`). Use `EXPLAIN` to show that PostgreSQL performs a sequential scan.
  4. Create a Full Index: Create a regular (full) index on the `active` column.
  5. Create a Partial Index: Create a partial index on `active` for only inactive buyers (`WHERE active = 0`).
  6. Query with Partial Index: Use `EXPLAIN` to see that PostgreSQL now utilizes the partial index when querying for inactive buyers.