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# Query interface
A `Query` sorts and filters the data at a Database location so only a subset of the child data is included. This can be used to order a collection of data by some attribute (for example, height of dinosaurs) as well as to restrict a large list of items (for example, chat messages) down to a number suitable for synchronizing to the client. Queries are created by chaining together one or more of the filter methods defined here.

Just as with a `DatabaseReference`<!-- -->, you can receive data from a `Query` by using the `on*()` methods. You will only receive events and `DataSnapshot`<!-- -->s for the subset of the data that matches your query.

See [https://firebase.google.com/docs/database/web/lists-of-data\#sorting\_and\_filtering\_data](https://firebase.google.com/docs/database/web/lists-of-data#sorting_and_filtering_data) for more information.

<b>Signature:</b>

```typescript
export declare interface Query 
```

## Properties

|  Property | Type | Description |
|  --- | --- | --- |
|  [ref](./database.query.md#queryref) | [DatabaseReference](./database.databasereference.md#databasereference_interface) | The <code>DatabaseReference</code> for the <code>Query</code>'s location. |

## Methods

|  Method | Description |
|  --- | --- |
|  [isEqual(other)](./database.query.md#queryisequal) | Returns whether or not the current and provided queries represent the same location, have the same query parameters, and are from the same instance of <code>FirebaseApp</code>.<!-- -->Two <code>DatabaseReference</code> objects are equivalent if they represent the same location and are from the same instance of <code>FirebaseApp</code>.<!-- -->Two <code>Query</code> objects are equivalent if they represent the same location, have the same query parameters, and are from the same instance of <code>FirebaseApp</code>. Equivalent queries share the same sort order, limits, and starting and ending points. |
|  [toJSON()](./database.query.md#querytojson) | Returns a JSON-serializable representation of this object. |
|  [toString()](./database.query.md#querytostring) | Gets the absolute URL for this location.<!-- -->The <code>toString()</code> method returns a URL that is ready to be put into a browser, curl command, or a <code>refFromURL()</code> call. Since all of those expect the URL to be url-encoded, <code>toString()</code> returns an encoded URL.<!-- -->Append '.json' to the returned URL when typed into a browser to download JSON-formatted data. If the location is secured (that is, not publicly readable), you will get a permission-denied error. |

## Query.ref

The `DatabaseReference` for the `Query`<!-- -->'s location.

<b>Signature:</b>

```typescript
readonly ref: DatabaseReference;
```

## Query.isEqual()

Returns whether or not the current and provided queries represent the same location, have the same query parameters, and are from the same instance of `FirebaseApp`<!-- -->.

Two `DatabaseReference` objects are equivalent if they represent the same location and are from the same instance of `FirebaseApp`<!-- -->.

Two `Query` objects are equivalent if they represent the same location, have the same query parameters, and are from the same instance of `FirebaseApp`<!-- -->. Equivalent queries share the same sort order, limits, and starting and ending points.

<b>Signature:</b>

```typescript
isEqual(other: Query | null): boolean;
```

#### Parameters

|  Parameter | Type | Description |
|  --- | --- | --- |
|  other | [Query](./database.query.md#query_interface) \| null | The query to compare against. |

<b>Returns:</b>

boolean

Whether or not the current and provided queries are equivalent.

## Query.toJSON()

Returns a JSON-serializable representation of this object.

<b>Signature:</b>

```typescript
toJSON(): string;
```
<b>Returns:</b>

string

A JSON-serializable representation of this object.

## Query.toString()

Gets the absolute URL for this location.

The `toString()` method returns a URL that is ready to be put into a browser, curl command, or a `refFromURL()` call. Since all of those expect the URL to be url-encoded, `toString()` returns an encoded URL.

Append '.json' to the returned URL when typed into a browser to download JSON-formatted data. If the location is secured (that is, not publicly readable), you will get a permission-denied error.

<b>Signature:</b>

```typescript
toString(): string;
```
<b>Returns:</b>

string

The absolute URL for this location.