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unique_key

snapshots/<filename>.sql
{{ config(
  unique_key="column_name"
) }}

dbt_project.yml
snapshots:
  <resource-path>:
    +unique_key: column_name_or_expression

Description​

A column name or expression that is unique for the inputs of a snapshot. dbt uses this to match records between a result set and an existing snapshot, so that changes can be captured correctly.

caution

Providing a non-unique key will result in unexpected snapshot results. dbt will not test the uniqueness of this key, consider testing the source data to ensure that this key is indeed unique.

Default​

This is a required parameter. No default is provided.

Examples​

Use an id column as a unique key​

snapshots/<filename>.sql
{{
    config(
      unique_key="id"
    )
}}

You can also write this in yaml. This might be a good idea if multiple snapshots share the same unique_key (though we prefer to apply this configuration in a config block, as above).

dbt_project.yml
snapshots:
  <resource-path>:
    +unique_key: id

Use a combination of two columns as a unique key​

This configuration accepts a valid column expression. As such, you can concatenate two columns together as a unique key if required. It's a good idea to use a separator (e.g. '-') to ensure uniqueness.

snapshots/transaction_items_snapshot.sql
{% snapshot transaction_items_snapshot %}

    {{
        config(
          unique_key="transaction_id||'-'||line_item_id",
          ...
        )
    }}

select
    transaction_id||'-'||line_item_id as id,
    *
from {{ source('erp', 'transactions') }}

{% endsnapshot %}

Though, it's probably a better idea to construct this column in your query and use that as the unique_key:

snapshots/transaction_items_snapshot.sql

{% snapshot transaction_items_snapshot %}

    {{
        config(
          unique_key="id",
          ...
        )
    }}

select
    transaction_id || '-' || line_item_id as id,
    *
from {{ source('erp', 'transactions') }}

{% endsnapshot %}


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