# IS \[ NOT ]

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Tests whether two values are equal or unequal, treating NULL as equal to NULL.

## Syntax

```scopeql
<left> IS <right>
<left> IS NOT <right>
```

## Arguments

| Argument  | Type                     | Description                                       |
| --------- | ------------------------ | ------------------------------------------------- |
| `<left>`  | Any type                 | First value to compare.                           |
| `<right>` | Compatible with `<left>` | Second value to compare. Either side may be NULL. |

## Returns

Returns `boolean`, never NULL.

* Both inputs are NULL: `IS` returns TRUE; `IS NOT` returns FALSE.
* Only one input is NULL: `IS` returns FALSE; `IS NOT` returns TRUE.
* Neither input is NULL: `IS` works like `=`; `IS NOT` works like `!=`.

Unlike `IS`, ordinary equality (`=`) returns NULL if either operand is NULL.

## Examples

Check whether each checkout event has a campaign value:

```scopeql
VALUES ('evt-17', 'spring'), ('evt-42', NULL), ('evt-63', 'loyalty')
SELECT $0 AS event_id, $1 AS campaign
SELECT event_id, campaign, campaign IS NULL AS missing, campaign IS NOT NULL AS present
```

```text
+----------+----------+---------+---------+
| event_id | campaign | missing | present |
+----------+----------+---------+---------+
| evt-17   | spring   | false   | true    |
| evt-42   | NULL     | true    | false   |
| evt-63   | loyalty  | false   | true    |
+----------+----------+---------+---------+
```