About incremental strategy

There are various strategies to implement the concept of incremental materializations. The value of each strategy depends on:

• The volume of data.
• The reliability of your unique_key.
• The support of certain features in your data platform.

An optional incremental_strategy config is provided in some adapters that controls the code that dbt uses to build incremental models.

Supported incremental strategies by adapter

Click the name of the adapter in the below table for more information about supported incremental strategies.

The merge strategy is available in dbt-postgres and dbt-redshift beginning in dbt v1.6.

Snowflake Configurations

dbt has changed the default materialization for incremental table merges from temporary table to view. For more information about this change and instructions for setting the configuration to a temp table, please read about Snowflake temporary tables.

Configuring incremental strategy

The incremental_strategy config can either be defined in specific models or for all models in your dbt_project.yml file:

dbt_project.yml

models:
  +incremental_strategy: "insert_overwrite"

or:

models/my_model.sql

{{
  config(
    materialized='incremental',
    unique_key='date_day',
    incremental_strategy='delete+insert',
    ...
  )
}}

select ...

Strategy-specific configs

If you use the merge strategy and specify a unique_key, by default, dbt will entirely overwrite matched rows with new values.

On adapters which support the merge strategy (including Snowflake, BigQuery, Apache Spark, and Databricks), you may optionally pass a list of column names to a merge_update_columns config. In that case, dbt will update only the columns specified by the config, and keep the previous values of other columns.

models/my_model.sql

{{
  config(
    materialized = 'incremental',
    unique_key = 'id',
    merge_update_columns = ['email', 'ip_address'],
    ...
  )
}}

select ...

Alternatively, you can specify a list of columns to exclude from being updated by passing a list of column names to a merge_exclude_columns config.

models/my_model.sql

{{
  config(
    materialized = 'incremental',
    unique_key = 'id',
    merge_exclude_columns = ['created_at'],
    ...
  )
}}

select ...

About incremental_predicates

incremental_predicates is an advanced use of incremental models, where data volume is large enough to justify additional investments in performance. This config accepts a list of any valid SQL expression(s). dbt does not check the syntax of the SQL statements.

This an example of a model configuration in a yml file you might expect to see on Snowflake:

models:
  - name: my_incremental_model
    config:
      materialized: incremental
      unique_key: id
      # this will affect how the data is stored on disk, and indexed to limit scans
      cluster_by: ['session_start']  
      incremental_strategy: merge
      # this limits the scan of the existing table to the last 7 days of data
      incremental_predicates: ["DBT_INTERNAL_DEST.session_start > dateadd(day, -7, current_date)"]
      # `incremental_predicates` accepts a list of SQL statements. 
      # `DBT_INTERNAL_DEST` and `DBT_INTERNAL_SOURCE` are the standard aliases for the target table and temporary table, respectively, during an incremental run using the merge strategy. 

Alternatively, here are the same configurations configured within a model file:

-- in models/my_incremental_model.sql

{{
  config(
    materialized = 'incremental',
    unique_key = 'id',
    cluster_by = ['session_start'],  
    incremental_strategy = 'merge',
    incremental_predicates = [
      "DBT_INTERNAL_DEST.session_start > dateadd(day, -7, current_date)"
    ]
  )
}}

...

This will template (in the dbt.log file) a merge statement like:

merge into <existing_table> DBT_INTERNAL_DEST
    from <temp_table_with_new_records> DBT_INTERNAL_SOURCE
    on
        -- unique key
        DBT_INTERNAL_DEST.id = DBT_INTERNAL_SOURCE.id
        and
        -- custom predicate: limits data scan in the "old" data / existing table
        DBT_INTERNAL_DEST.session_start > dateadd(day, -7, current_date)
    when matched then update ...
    when not matched then insert ...

Limit the data scan of upstream tables within the body of their incremental model SQL, which will limit the amount of "new" data processed/transformed.

with large_source_table as (

    select * from {{ ref('large_source_table') }}
    {% if is_incremental() %}
        where session_start >= dateadd(day, -3, current_date)
    {% endif %}

),

...

info

The syntax depends on how you configure your incremental_strategy:

• If using the merge strategy, you may need to explicitly alias any columns with either DBT_INTERNAL_DEST ("old" data) or DBT_INTERNAL_SOURCE ("new" data).
• There's a decent amount of conceptual overlap with the insert_overwrite incremental strategy.

Built-in strategies

Before diving into custom strategies, it's important to understand the built-in incremental strategies in dbt and their corresponding macros:

incremental_strategy	Corresponding macro
append	get_incremental_append_sql
delete+insert	get_incremental_delete_insert_sql
merge	get_incremental_merge_sql
insert_overwrite	get_incremental_insert_overwrite_sql

For example, a built-in strategy for the append can be defined and used with the following files:

macros/append.sql

{% macro get_incremental_append_sql(arg_dict) %}

  {% do return(some_custom_macro_with_sql(arg_dict["target_relation"], arg_dict["temp_relation"], arg_dict["unique_key"], arg_dict["dest_columns"], arg_dict["incremental_predicates"])) %}

{% endmacro %}


{% macro some_custom_macro_with_sql(target_relation, temp_relation, unique_key, dest_columns, incremental_predicates) %}

    {%- set dest_cols_csv = get_quoted_csv(dest_columns | map(attribute="name")) -%}

    insert into {{ target_relation }} ({{ dest_cols_csv }})
    (
        select {{ dest_cols_csv }}
        from {{ temp_relation }}
    )

{% endmacro %}

Define a model models/my_model.sql:

{{ config(
    materialized="incremental",
    incremental_strategy="append",
) }}

select * from {{ ref("some_model") }}

Custom strategies

Starting from dbt version 1.2 and onwards, users have an easier alternative to creating an entirely new materialization. They define and use their own "custom" incremental strategies by:

1. Defining a macro named get_incremental_STRATEGY_sql. Note that STRATEGY is a placeholder and you should replace it with the name of your custom incremental strategy.
2. Configuring incremental_strategy: STRATEGY within an incremental model.

dbt won't validate user-defined strategies, it will just look for the macro by that name, and raise an error if it can't find one.

For example, a user-defined strategy named insert_only can be defined and used with the following files:

macros/my_custom_strategies.sql

{% macro get_incremental_insert_only_sql(arg_dict) %}

  {% do return(some_custom_macro_with_sql(arg_dict["target_relation"], arg_dict["temp_relation"], arg_dict["unique_key"], arg_dict["dest_columns"], arg_dict["incremental_predicates"])) %}

{% endmacro %}


{% macro some_custom_macro_with_sql(target_relation, temp_relation, unique_key, dest_columns, incremental_predicates) %}

    {%- set dest_cols_csv = get_quoted_csv(dest_columns | map(attribute="name")) -%}

    insert into {{ target_relation }} ({{ dest_cols_csv }})
    (
        select {{ dest_cols_csv }}
        from {{ temp_relation }}
    )

{% endmacro %}

models/my_model.sql

{{ config(
    materialized="incremental",
    incremental_strategy="insert_only",
    ...
) }}

...

Custom strategies from a package

To use the merge_null_safe custom incremental strategy from the example package:

• Install the package
• Add the following macro to your project:

macros/my_custom_strategies.sql

{% macro get_incremental_merge_null_safe_sql(arg_dict) %}
    {% do return(example.get_incremental_merge_null_safe_sql(arg_dict)) %}
{% endmacro %}

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