# query()

This operation conducts a scalar filtering with a specified boolean expression.

```java
public QueryResp query(QueryReq request)
```

## Request Syntax

```java
query(QueryReq.builder()
    .collectionName(String collectionName)
    .partitionNames(List<String> partitionNames)
    .outputFields(List<String> outputFields)
    .ids(List<Object> ids)
    .filter(String filter)
    .consistencyLevel(ConsistencyLevel consistencyLevel)
    .offset(long offset)
    .limit(long limit)
    .build()
)
```

**BUILDER METHODS:**

- `collectionName(String collectionName)`

    The name of an existing collection.

- `partitionNames(List<String> partitionNames)`

    A list of partition names.

- `outputFields(List<String> outputFields)`

    A list of field names to include in each entity in return.

    The value defaults to **None**. If left unspecified, all fields in the collection are selected as the output fields.

- `ids(List<Object> ids)`

    The IDs of entities to query.

- `filter(String filter)`

    A scalar filtering condition to filter matching entities. 

    You can set this parameter to an empty string to skip scalar filtering. To build a scalar filtering condition, refer to [Boolean Expression Rules](https://milvus.io/docs/boolean.md). 

- `consistencyLevel([ConsistencyLevel](../Collections/ConsistencyLevel.md) consistencyLevel)`

    The consistency level of the target collection.

    The value defaults to the one specified when you create the current collection, with options of **Strong** (**0**), **Bounded** (**1**), **Session** (**2**), and **Eventually** (**3**).

    <div class="admonition note">

    <p><b>what is the consistency level?</b></p>

    <p>Consistency in a distributed database specifically refers to the property that ensures every node or replica has the same view of data when writing or reading data at a given time.</p>
    <p>Milvus supports four consistency levels: <strong>Strong</strong>, <strong>Bounded Staleness</strong>, <strong>Session</strong>, and <strong>Eventually</strong>. The default consistency level in Milvus is <strong>Bounded Staleness</strong>.</p>
    <p>You can easily tune the consistency level when conducting a vector similarity search or query to make it best suit your application.</p>

    </div>

- `offset(long offset)`

    The number of records to skip in the query result. 

    You can use this parameter in combination with `limit` to enable pagination.

    The sum of this value and `limit` should be less than 16,384. 

- `limit(long limit)`

    The number of records to return in the query result.

    You can use this parameter in combination with `offset` to enable pagination.

    The sum of this value and `offset` should be less than 16,384. 

**RETURN TYPE:**

*QueryResp*

**RETURNS:**

A **QueryResp object representing specific query results with the specified output fields

**PARAMETERS:**

- queryResults(List\&lt;QueryResp.QueryResult\&gt;)

A list of QueryResult objects with each QueryResult representing a queried entity.

<div class="admonition note">

<p><b>notes</b></p>

<p>If the number of returned entities is less than expected, duplicate entities may exist in your collection.</p>

</div>

**EXCEPTIONS:**

- **MilvusClientExceptions**

    This exception will be raised when any error occurs during this operation.

## Example

```java
import io.milvus.v2.client.ConnectConfig;
import io.milvus.v2.client.MilvusClientV2;
import io.milvus.v2.service.vector.request.QueryReq;
import io.milvus.v2.service.vector.response.QueryResp;

// 1. Set up a client
ConnectConfig connectConfig = ConnectConfig.builder()
        .uri("http://localhost:19530")
        .token("root:Milvus")
        .build();
        
MilvusClientV2 client = new MilvusClientV2(connectConfig);

// 2. Query by filter "id < 10"
QueryReq queryReq = QueryReq.builder()
        .collectionName("test")
        .filter("id < 10")
        .build();
QueryResp queryResp = client.query(queryReq);
for (QueryResp.QueryResult result : queryResp.getGetResults()) {
    System.out.println(result.getEntity());
}
```