---
title: Query fields and tags
description: Use the filter() function to query data based on fields, tags, or any other column value. filter() performs operations similar to the SELECT statement and the WHERE clause in InfluxQL and other SQL-like query languages.
url: https://docs.influxdata.com/influxdb/v1/flux/guides/query-fields/
estimated_tokens: 1493
product: InfluxDB OSS v1
version: v1
---

# Query fields and tags

This page documents an earlier version of InfluxDB OSS. [InfluxDB 3 Core](/influxdb3/core/) is the latest stable version.

Use the [`filter()` function](/flux/v0/stdlib/universe/filter/) to query data based on fields, tags, or any other column value. `filter()` performs operations similar to the `SELECT` statement and the `WHERE` clause in InfluxQL and other SQL-like query languages.

## The filter() function

`filter()` has an `fn` parameter that expects a **predicate function**, an anonymous function comprised of one or more **predicate expressions**. The predicate function evaluates each input row. Rows that evaluate to `true` are **included** in the output data. Rows that evaluate to `false` are **excluded** from the output data.

```js
// ...
  |> filter(fn: (r) => r._measurement == "example-measurement" )
```

The `fn` predicate function requires an `r` argument, which represents each row as `filter()` iterates over input data. Key-value pairs in the row record represent columns and their values. Use **dot notation** or **bracket notation** to reference specific column values in the predicate function. Use [logical operators](/flux/v0/language/operators/#logical-operators) to chain multiple predicate expressions together.

```js
// Row record
r = {foo: "bar", baz: "quz"}

// Example predicate function
(r) => r.foo == "bar" and r["baz"] == "quz"

// Evaluation results
(r) => true and true
```

## Filter by fields and tags

The combination of [`from()`](/flux/v0/stdlib/influxdata/influxdb/from/), [`range()`](/flux/v0/stdlib/universe/range), and `filter()` represent the most basic Flux query:

1. Use `from()` to define your [bucket](/influxdb/v1/flux/get-started/#buckets).
2. Use `range()` to limit query results by time.
3. Use `filter()` to identify what rows of data to output.

```js
from(bucket: "db/rp")
  |> range(start: -1h)
  |> filter(fn: (r) =>
      r._measurement == "example-measurement" and
      r._field == "example-field" and
      r.tag == "example-tag"
  )
```