# schema

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

Summarizes the top-level keys and value types observed in objects.

## Syntax

```scopeql
schema(<object>)
```

## Arguments

| Argument   | Type     | Description                                                     |
| ---------- | -------- | --------------------------------------------------------------- |
| `<object>` | `object` | Objects to inspect. Cast an `any` expression to `object` first. |

## Returns

Returns an `array` of objects. Each object describes an observed field:

* `key`: the field name.
* `type`: its value type.
* `elements`: distinct element types, present only for array fields.

A key appears more than once when its value type or array element types differ across input objects.

Ignores NULL input objects. Returns `[]` when no keys are observed. Result order is unspecified.

## Examples

### Inspect changing event payloads

Inspect a sample of checkout payloads before writing typed queries. Here a producer starts sending `amount` as text and introduces a `coupon` field.

```scopeql
VALUES
    ({'amount': 49.0, 'channel': 'web'}),
    ({'amount': '79.00', 'channel': 'mobile', 'coupon': 'WELCOME'})
SELECT $0 AS payload
AGGREGATE schema(payload) AS fields
```

The `fields` value:

```text
[
  {
    "key": "amount",
    "type": "float"
  },
  {
    "key": "amount",
    "type": "string"
  },
  {
    "key": "channel",
    "type": "string"
  },
  {
    "key": "coupon",
    "type": "string"
  }
]
```

`amount` appears as both `float` and `string`; cast it before calculating totals. Field order may vary.

### Inspect array element types

The item list is still an array in both payloads, but one producer sends a numeric item ID. Inspect the element types as well as the outer type.

```scopeql
VALUES
    ({'item_ids': ['sku-17', 'sku-42']}),
    ({'item_ids': ['sku-63', 84]})
SELECT $0 AS payload
AGGREGATE schema(payload) AS fields
```

The `fields` value:

```text
[
  {
    "elements": [
      "string"
    ],
    "key": "item_ids",
    "type": "array"
  },
  {
    "elements": [
      "int",
      "string"
    ],
    "key": "item_ids",
    "type": "array"
  }
]
```

The second entry includes both `int` and `string` elements. Entry and element-type order may vary.