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# N + 1 problem

## Introduction

* The N+1 query problem happens when your code executes N additional query statements to fetch the same data that could have been retrieved when executing the primary query.

## Example

```sql
SELECT "cookies".* FROM "cookies"
SELECT "toppings".* FROM "toppings" WHERE "toppings"."cookie_id" = 1
SELECT "toppings".* FROM "toppings" WHERE "toppings"."cookie_id" = 2
SELECT "toppings".* FROM "toppings" WHERE "toppings"."cookie_id" = 3
```

* N = fetch the list of topping based on number of cookies
* 1 = fetch the list of cookies

## Solution

```sql
SELECT "cookies".* FROM "cookies"
SELECT "toppings".* FROM "toppings" WHERE "toppings"."cookie_id" IN (1, 2, 3)
```

## References

{% embed url="<https://medium.com/doctolib/understanding-and-fixing-n-1-query-30623109fe89>" %}