Add merge_update_columns config

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## dbt-spark 0.20.0 (Release TBD)
 
+### Features
+
+- Add support for `merge_update_columns` config in `merge`-strategy incremental models ([#183](https://github.com/fishtown-analytics/dbt-spark/pull/183), ([#184](https://github.com/fishtown-analytics/dbt-spark/pull/184))
+
 ### Fixes
 
 - Fix column-level `persist_docs` on Delta tables, add tests ([#180](https://github.com/fishtown-analytics/dbt-spark/pull/180))

dbt/adapters/spark/impl.py

@@ -37,6 +37,7 @@ class SparkConfig(AdapterConfig):
     clustered_by: Optional[Union[List[str], str]] = None
     buckets: Optional[int] = None
     options: Optional[Dict[str, str]] = None
+    merge_update_columns: Optional[str] = None
 
 
 class SparkAdapter(SQLAdapter):

dbt/include/spark/macros/materializations/incremental/strategies.sql

@@ -20,7 +20,8 @@
 
 
 {% macro spark__get_merge_sql(target, source, unique_key, dest_columns, predicates=none) %}
-  {# ignore dest_columns - we will just use `*` #}
+  {# skip dest_columns, use merge_update_columns config if provided, otherwise use "*" #}
+  {%- set update_columns = config.get("merge_update_columns") -%}
 
   {% set merge_condition %}
     {% if unique_key %}
@@ -32,8 +33,16 @@
 
     merge into {{ target }} as DBT_INTERNAL_DEST
       using {{ source.include(schema=false) }} as DBT_INTERNAL_SOURCE
+
       {{ merge_condition }}
-      when matched then update set *
+
+      when matched then update set
+        {% if update_columns -%}{%- for column_name in update_columns %}
+            {{ column_name }} = DBT_INTERNAL_SOURCE.{{ column_name }}
+            {%- if not loop.last %}, {%- endif %}
+        {%- endfor %}
+        {%- else %} * {% endif %}
+
       when not matched then insert *
 {% endmacro %}
 

test/custom/incremental_strategies/data/expected_partial_upsert.csv

@@ -0,0 +1,4 @@
+id,msg,color
+1,hello,blue
+2,yo,red
+3,anyway,purple

test/custom/incremental_strategies/models_delta/merge_update_columns.sql

@@ -0,0 +1,22 @@
+{{ config(
+    materialized = 'incremental',
+    incremental_strategy = 'merge',
+    file_format = 'delta',
+    unique_key = 'id',
+    merge_update_columns = ['msg'],
+) }}
+
+{% if not is_incremental() %}
+
+select cast(1 as bigint) as id, 'hello' as msg, 'blue' as color
+union all
+select cast(2 as bigint) as id, 'goodbye' as msg, 'red' as color
+
+{% else %}
+
+-- msg will be updated, color will be ignored
+select cast(2 as bigint) as id, 'yo' as msg, 'green' as color
+union all
+select cast(3 as bigint) as id, 'anyway' as msg, 'purple' as color
+
+{% endif %}

test/custom/incremental_strategies/test_incremental_strategies.py

@@ -71,6 +71,7 @@ def run_and_test(self):
         self.assertTablesEqual("append_delta", "expected_append")
         self.assertTablesEqual("merge_no_key", "expected_append")
         self.assertTablesEqual("merge_unique_key", "expected_upsert")
+        self.assertTablesEqual("merge_update_columns", "expected_partial_upsert")
 
     @use_profile("databricks_cluster")
     def test_delta_strategies_databricks_cluster(self):