In this technical blog, we will explore the impact of indexes on query performance in PostgreSQL. We will start by analyzing a query that does not utilize indexes efficiently and examine the execution plan using the EXPLAIN statement. We will then demonstrate the effectiveness of indexes by modifying the query to utilize them and comparing the improved execution plan and performance.

Query without Indexes:

Consider the following example query that retrieves data from a large table without utilizing indexes efficiently:

FROM sales
WHERE customer_id = 12345
AND order_date > ‘2022-01-01’;

Explanation of the Execution Plan:

To analyze the query’s execution plan, we can use the EXPLAIN statement. Running EXPLAIN on the above query provides insights into the query plan and identifies any potential performance issues, such as sequential scans or lack of index usage.

Query Plan (Without Indexes):

Seq Scan on sales (cost=0.00..1000.00 rows=100 width=4)
Filter: ((customer_id = 12345) AND (order_date > ‘2022-01-01’::date))

This execution plan shows that the query performs a sequential scan on the entire “sales” table, filtering rows based on the given conditions. Without indexes, the database has to scan every row, resulting in slower query performance, especially with large tables.

Adding Indexes for Improved Performance:

To optimize the query, we can create indexes on the columns involved in the WHERE clause, namely “customer_id” and “order_date.” Indexes allow the database to quickly locate the relevant rows, significantly improving query performance.

CREATE INDEX idx_sales_customer_id ON sales (customer_id);
CREATE INDEX idx_sales_order_date ON sales (order_date);

Query Plan (With Indexes):

Index Scan using idx_sales_customer_id on sales (cost=0.00..10.00 rows=10 width=4)
Index Cond: (customer_id = 12345)
Filter: (order_date > ‘2022-01-01’::date)

With the added indexes, the execution plan changes to an Index Scan using the “idx_sales_customer_id” index. The index condition filters rows based on the “customer_id,” significantly reducing the number of rows scanned. The subsequent filter condition on “order_date” is also applied efficiently.


Indexes play a crucial role in optimizing query performance in PostgreSQL. By creating appropriate indexes on the columns involved in the WHERE clause, we can greatly enhance query execution speed and overall database performance. Analyzing the execution plan using EXPLAIN helps identify areas for optimization and ensures efficient use of indexes.

By leveraging the power of indexes, we can unlock the full potential of PostgreSQL and achieve significant performance improvements in our queries.

Remember, the key to effective indexing lies in understanding your data, query patterns, and optimizing indexes based on specific requirements.

Stay tuned for more PostgreSQL optimization techniques and best practices!