# lookupContains operator

The `lookupContains` operator checks whether a key exists in a lookup table and returns a boolean value.

You can use it as a condition inside a `where` or `if` expression in FuseQL.

## Syntax

```fuseql
... | where lookupContains(<lookupTableName>, <event-field>=<lookup-field>) | ...
```

- `<lookupTableName>` — Name of the lookup table in Kloudfuse.
- `<event-field>` — A log field to check against. This can be a facet, a label, or a field extracted using the `parse` operator.
- `<lookup-field>` — A field in the lookup table used for matching.

## Example

Check if the `user_id` field in logs exists in the lookup table `vip_users`:

```fuseql
logs
| where lookupContains(vip_users, user_id=id)
```

This query filters logs to only include events where `user_id` matches the `id` field in the `vip_users` lookup table.