# strategy

### timestamp

(Applies to dbt v1.9 and later)

snapshots/\<filename>.yml

```yaml
snapshots:
- name: snapshot_name:
  relation: source('my_source', 'my_table')
  config:
    strategy: timestamp
    updated_at: column_name
```

dbt\_project.yml

```yml
snapshots:
  <resource-path>:
    +strategy: timestamp
    +updated_at: column_name
```

### check

(Applies to dbt v1.9 and later)

snapshots/\<filename>.yml

```yaml
snapshots:
- name: snapshot_name:
  relation: source('my_source', 'my_table')
  config:
    strategy: check
    check_cols: [column_name] | "all"
```

dbt\_project.yml

```yml
snapshots:
  <resource-path>:
    +strategy: check
    +check_cols: [column_name] | all
```

## Description

The snapshot strategy dbt should use to detect record changes. Read the guide to [snapshots](../../docs/build/snapshots.md#detecting-row-changes) to understand the differences between the two.

## Default

This is a **required configuration**. There is no default value.

## Examples

### Use the timestamp strategy

(Applies to dbt v1.9 and later)

snapshots/timestamp\_example.yml

```yaml
snapshots:
  - name: orders_snapshot_timestamp
    relation: source('jaffle_shop', 'orders')
    config:
      schema: snapshots
      strategy: timestamp
      unique_key: id
      updated_at: updated_at
```

### Use the check strategy

(Applies to dbt v1.9 and later)

snapshots/check\_example.yml

```yaml
snapshots:
  - name: orders_snapshot_check
    relation: source('jaffle_shop', 'orders')
    config:
      schema: snapshots
      unique_key: id
      strategy: check
      check_cols:
        - status
        - is_cancelled
```

### Advanced: define and use custom snapshot strategy

Behind the scenes, snapshot strategies are implemented as macros, named `snapshot_<strategy>_strategy`

* [Source code](https://github.com/dbt-labs/dbt-adapters/blob/60005a0a2bd33b61cb65a591bc1604b1b3fd25d5/dbt/include/global_project/macros/materializations/snapshots/strategies.sql#L52) for the timestamp strategy
* [Source code](https://github.com/dbt-labs/dbt-adapters/blob/60005a0a2bd33b61cb65a591bc1604b1b3fd25d5/dbt/include/global_project/macros/materializations/snapshots/strategies.sql#L136) for the check strategy

It's possible to implement your own snapshot strategy by adding a macro with the same naming pattern to your project. For example, you might choose to create a strategy which records hard deletes, named `timestamp_with_deletes`.

1. Create a macro named `snapshot_timestamp_with_deletes_strategy`. Use the existing code as a guide and adjust as needed.
2. Use this strategy via the `strategy` configuration:

(Applies to dbt v1.9 and later)

snapshots/\<filename>.yml

```yaml
snapshots:
  - name: my_custom_snapshot
    relation: source('my_source', 'my_table')
    config:
      strategy: timestamp_with_deletes
      updated_at: updated_at_column
      unique_key: id
```

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