# Efficient use of Query Builder

## Avoiding the N+1 Query Problem[​](#avoiding-the-n1-query-problem "Direct link to Avoiding the N+1 Query Problem")

The N+1 Query Problem occurs when the system executes too many sub-queries for each row of data retrieved.

To avoid this, you can use `leftJoinAndSelect` or `innerJoinAndSelect` to combine tables in a single query instead of executing multiple queries.

```
const users = await dataSource

    .getRepository(User)

    .createQueryBuilder("user")

    .leftJoinAndSelect("user.posts", "post")

    .getMany()
```

Here, `leftJoinAndSelect` helps retrieve all user posts in a single query rather than many small queries.

## Use `getRawMany()` when only raw data is needed[​](#use-getrawmany-when-only-raw-data-is-needed "Direct link to use-getrawmany-when-only-raw-data-is-needed")

In cases where full objects aren't required, you can use `getRawMany()` to fetch raw data and avoid TypeORM processing too much information.

```
const rawPosts = await dataSource

    .getRepository(Post)

    .createQueryBuilder("post")

    .select("post.title, post.createdAt")

    .getRawMany()
```

## Limit fields using `select`[​](#limit-fields-using-select "Direct link to limit-fields-using-select")

To optimize memory usage and reduce unnecessary data, select only the required fields using `select`.

```
const users = await dataSource

    .getRepository(User)

    .createQueryBuilder("user")

    .select(["user.name", "user.email"])

    .getMany()
```