references/query-covering-indexes.md

---
title: Use Covering Indexes to Avoid Table Lookups
impact: MEDIUM-HIGH
impactDescription: 2-5x faster queries by eliminating heap fetches
tags: indexes, covering-index, include, index-only-scan
---

## Use Covering Indexes to Avoid Table Lookups

Covering indexes include all columns needed by a query, enabling index-only scans that skip the table entirely.

**Incorrect (index scan + heap fetch):**

```sql
create index users_email_idx on users (email);

-- Must fetch name and created_at from table heap
select email, name, created_at from users where email = 'user@example.com';
```

**Correct (index-only scan with INCLUDE):**

```sql
-- Include non-searchable columns in the index
create index users_email_idx on users (email) include (name, created_at);

-- All columns served from index, no table access needed
select email, name, created_at from users where email = 'user@example.com';
```

Use INCLUDE for columns you SELECT but don't filter on:

```sql
-- Searching by status, but also need customer_id and total
create index orders_status_idx on orders (status) include (customer_id, total);

select status, customer_id, total from orders where status = 'shipped';
```

Reference: [Index-Only Scans](https://www.postgresql.org/docs/current/indexes-index-only-scans.html)