# max\_by

[Read this page in HTML](https://www.scopedb.io/docs/reference/functions/aggregate/max_by)

Returns a value from the row with the maximum comparison key.

## Syntax

```scopeql
max_by(<value>, <key>)
```

## Arguments

| Argument  | Type                  | Description                                               |
| --------- | --------------------- | --------------------------------------------------------- |
| `<value>` | Any type              | Expression to return from the selected row. May be NULL.  |
| `<key>`   | Any type except `any` | Expression used to select the row. NULL keys are ignored. |

## Returns

Returns the same type as `<value>`. Returns NULL if there is no non-NULL key. If keys tie, any tied row may be selected.

## Examples

### Keep the details of the slowest request

Find the slowest request per service and retain its ID and status together in one object.

```scopeql
VALUES
    ('checkout', 'req-101', 200, 95), ('checkout', 'req-102', 504, 1200),
    ('catalog', 'req-201', 200, 25), ('catalog', 'req-202', 200, 140)
SELECT $0 AS service, $1 AS request_id, $2 AS status, $3 AS latency_ms
GROUP BY service
AGGREGATE max_by({'request_id': request_id, 'status': status}, latency_ms) AS request
ORDER BY service
```

```text
+----------+---------------------------------------+
| service  | request                               |
+----------+---------------------------------------+
| catalog  | {"request_id":"req-202","status":200} |
| checkout | {"request_id":"req-102","status":504} |
+----------+---------------------------------------+
```

### Read the latest order status

Use the event timestamp as the comparison key to retrieve the latest known state of each order.

```scopeql
VALUES
    ('o-17', '2026-06-01T10:02:00Z', 'paid'),
    ('o-17', '2026-06-01T10:00:00Z', 'created'),
    ('o-42', '2026-06-01T10:01:00Z', 'created'),
    ('o-42', '2026-06-01T10:04:00Z', 'cancelled')
SELECT $0 AS order_id, $1::timestamp AS event_time, $2 AS status
GROUP BY order_id
AGGREGATE max_by(status, event_time) AS latest_status
ORDER BY order_id
```

```text
+----------+---------------+
| order_id | latest_status |
+----------+---------------+
| o-17     | paid          |
| o-42     | cancelled     |
+----------+---------------+
```

If events share the latest timestamp, either status may be returned. Use [`DISTINCT ON ... BY`](https://www.scopedb.io/docs/reference/commands/stmt-query.md#distinct-on) with an additional sort key when ties need a defined order.