> ## Content Index
> Fetch the complete content index at: https://nolongerset.com/llms.txt
> Use this file to discover other available public pages before exploring further.

# What is a Covering Index?
- URL: https://nolongerset.com/under-100-covering-index/
- Published: 2021-08-27T02:04:58.000Z
- Updated: 2026-05-08T13:02:44.000Z
- Description: The concept of "covering indexes" explained in under 100 words. #Under100
- Author: Mike Wolfe
- Tags: Under 100, #Import 2026-05-20 02:59

In a typical index, the database uses the index to look up the primary key, which it then uses to look up the row in the original table. **Two lookups**.

![](https://storage.ghost.io/c/eb/d7/ebd732c1-5f03-4f07-b386-5d08557e15c9/content/images/2021/08/image-58.png)

If you only need a small subset of fields, you can save a lookup by creating a compound index that includes those fields.

![](https://storage.ghost.io/c/eb/d7/ebd732c1-5f03-4f07-b386-5d08557e15c9/content/images/2021/08/image-57.png)

An index is considered a *covering index* in the context of a SELECT statement that requires only the "covered"fields. Thus, the **CityName, Country** index *covers* the following SQL statement:

```sql
SELECT CityName, Country
FROM City
WHERE CityName = 'Berlin'
```

### Bottom Line

A covering index **saves a lookup**.

---

*Image by [esudroff](https://pixabay.com/users/esudroff-627167/?utm%5Fsource=link-attribution&utm%5Fmedium=referral&utm%5Fcampaign=image&utm%5Fcontent=1399332) from [Pixabay](https://pixabay.com/?utm%5Fsource=link-attribution&utm%5Fmedium=referral&utm%5Fcampaign=image&utm%5Fcontent=1399332)*