---
title: ClickHouse
---
# ClickHouse

Svix can deliver webhooks directly to a ClickHouse table, without your customers having to set up any listener endpoint or write any glue code.

When **Advanced Endpoint Types** is [enabled](/advanced-endpoints#enabling-advanced-endpoint-types), your customers will see the option to use a ClickHouse destination in the [App Portal](/app-portal).

![ClickHouse Endpoint Create](/img/advanced-endpoints/clickhouse-create.png)

They will be able to configure the connection right in the App Portal:

- `url` — the HTTP URL of your ClickHouse server (e.g. `https://my-clickhouse.example.com:8443`).
- `username`, `password` — the credentials used to authenticate.
- `tableName` — the table that receives the rows.
- `database` — the database that contains the table. Defaults to `default`.

Every batch of webhooks received by the endpoint is inserted into the configured ClickHouse table.

## Destination table

Without a transformation, Svix inserts each webhook's payload directly into the table using ClickHouse's [`JSONEachRow`](https://clickhouse.com/docs/interfaces/formats/JSONEachRow) format. The top-level fields of each payload must match the columns of your table.

The table must already exist before you enable the endpoint. For example, for payloads shaped like `{"email": "...", "username": "..."}`, create the table with:

```sql
CREATE TABLE events (
  email String,
  username String
)
ENGINE = MergeTree()
ORDER BY tuple();
```

Unlike some other warehouse destinations, ClickHouse does not add any columns of its own — you define the full schema, and the payload fields are matched to it by name.

# Transformations

If your payloads don't already match your table's columns, add a transformation that returns the `rows` to insert. Each row is an object whose keys match your table's columns.

```JavaScript
/**
 * @param input - The input object
 * @param input.events - The array of webhooks in the batch. The number of webhooks in the batch is capped by the endpoint's batch size.
 * @param input.events[].payload - The message payload (string or JSON)
 * @param input.events[].eventType - The message event type (string)
 *
 * @returns Object describing the rows to insert.
 * @returns returns.rows - The array of rows to insert. Each row is an object whose keys match the columns of your ClickHouse table.
 */
function handler(input) {
    const rows = input.events.map((event) => ({
        email: event.payload.address,
        username: event.payload.handle
    }));

    return { rows };
}
```

`input.events` is the list of webhooks received by the endpoint, processed in batches.

Each entry in the returned `rows` array is inserted as a separate row using `JSONEachRow`, so the object keys must match the column names of your table.

For example, if the endpoint receives the following messages:

```json
{
  "eventType": "user.created",
  "payload": "{\"address\": \"joe@enterprise.io\", \"handle\": \"joe\"}"
}
```

```json
{
  "eventType": "user.created",
  "payload": "{\"address\": \"amy@enterprise.io\", \"handle\": \"amy\"}"
}
```

The transformation above inserts two rows into your table, mapping each payload's `address` and `handle` fields onto the `email` and `username` columns.

| `email` | `username` |
| --- | --- |
| `joe@enterprise.io` | `joe` |
| `amy@enterprise.io` | `amy` |