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# REQUIRED_FILTER

Declares a filter that always applies.

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**Family:** [Filters](https://kater.ai/docs/sql-reference/functions/filters/)

A reader cannot switch it off.

## Syntax

```sql
WHERE
  REQUIRED_FILTER('name', condition, label='Label')
```

## Arguments

| Argument | Description |
| --- | --- |
| `name` | The filter's name, in quotes. |
| `condition` | The condition the filter applies, such as `KATER__IS_NOT_NULL(orders.region)`. It reads no parameters. |
| `label` | The name a reader sees, such as `'Region is set'`. |

## Returns

Nothing of its own. The query keeps only the rows where the condition is TRUE.

## Usage notes

- Write it as a direct `AND` condition of WHERE.
- A measure's required filters stay in force under every `EVAL` modifier, `CLEAR()` included.

## Example

This Sandbox query reads the sample shop's orders. The table shows the rows that Kater gave.

```sql {6}
SELECT
  orders.region AS "Region",
  EVAL(orders.count_distinct__order_id) AS "Orders"
FROM kater_dataset.orders AS orders
WHERE
  REQUIRED_FILTER('is_not_null__region', KATER__IS_NOT_NULL(orders.region), label='Region is set')
GROUP BY
  orders.region
ORDER BY
  1
```

| Region | Orders |
| --- | --- |
| AMER | 728 |
| APAC | 671 |
| EMEA | 777 |
| LATAM | 760 |

## See also

- [Filters and parameters](https://kater.ai/docs/model/filters-and-parameters/)
- Other functions in [Filters](https://kater.ai/docs/sql-reference/functions/filters/): [`OPTIONAL_FILTER`](https://kater.ai/docs/sql-reference/functions/optional_filter/)

On this page

Syntax
Arguments
Returns
Usage notes
Example
See also

Kater SQL Functions Filters

REQUIRED_FILTER

Declares a filter that always applies.

Family: Filters

A reader cannot switch it off.

Syntax

1
WHERE
2
  REQUIRED_FILTER('name', condition, label='Label')

Arguments

Argument	Description
`name`	The filter’s name, in quotes.
`condition`	The condition the filter applies, such as `KATER__IS_NOT_NULL(orders.region)`. It reads no parameters.
`label`	The name a reader sees, such as `'Region is set'`.

Returns

Nothing of its own. The query keeps only the rows where the condition is TRUE.

Usage notes

Write it as a direct AND condition of WHERE.
A measure’s required filters stay in force under every EVAL modifier, CLEAR() included.

Example

This Sandbox query reads the sample shop’s orders. The table shows the rows that Kater gave.

1
SELECT
2
  orders.region AS "Region",
3
  EVAL(orders.count_distinct__order_id) AS "Orders"
4
FROM kater_dataset.orders AS orders
5
WHERE
6
  REQUIRED_FILTER('is_not_null__region', KATER__IS_NOT_NULL(orders.region), label='Region is set')
7
GROUP BY
8
  orders.region
9
ORDER BY
10
  1

Region	Orders
AMER	728
APAC	671
EMEA	777
LATAM	760

See also

Filters and parameters
Other functions in Filters: OPTIONAL_FILTER