Add microbatch strategy

This work is basically in entirety a duplicate of the work done by
MichelleArk in dbt-labs/dbt-snowflake#1179.
I don't really expect this to work first try, but it might. I expect
to need to do some edits, but who knows, maybe I'll get lucky.

dbt/adapters/redshift/impl.py

@@ -155,7 +155,7 @@ def valid_incremental_strategies(self):
         """The set of standard builtin strategies which this adapter supports out-of-the-box.
         Not used to validate custom strategies defined by end users.
         """
-        return ["append", "delete+insert", "merge"]
+        return ["append", "delete+insert", "merge", "microbatch"]
 
     def timestamp_add_sql(self, add_to: str, number: int = 1, interval: str = "hour") -> str:
         return f"{add_to} + interval '{number} {interval}'"

dbt/include/redshift/macros/materializations/incremental_merge.sql

@@ -65,3 +65,34 @@
     )
 
 {% endmacro %}
+
+{% macro redshift__get_incremental_microbatch_sql(arg_dict) %}
+    {%- set target = arg_dict["target_relation"] -%}
+    {%- set source = arg_dict["temp_relation"] -%}
+    {%- set dest_columns = arg_dict["dest_columns"] -%}
+    {%- set incremental_predicates = [] if arg_dict.get('incremental_predicates') is none else arg_dict.get('incremental_predicates') -%}
+
+    {#-- Add additional incremental_predicates to filter for batch --#}
+    {% if model.config.get("__dbt_internal_microbatch_event_time_start") -%}
+        {% do incremental_predicates.append("DBT_INTERNAL_TARGET." ~ model.config.event_time ~ " >= TIMESTAMP '" ~ model.config.__dbt_internal_microbatch_event_time_start ~ "'") %}
+    {% endif %}
+    {% if model.config.__dbt_internal_microbatch_event_time_end -%}
+        {% do incremental_predicates.append("DBT_INTERNAL_TARGET." ~ model.config.event_time ~ " < TIMESTAMP '" ~ model.config.__dbt_internal_microbatch_event_time_end ~ "'") %}
+    {% endif %}
+    {% do arg_dict.update({'incremental_predicates': incremental_predicates}) %}
+
+    delete from {{ target }} DBT_INTERNAL_TARGET
+    using {{ source }}
+    where (
+    {% for predicate in incremental_predicates %}
+        {%- if not loop.first %}and {% endif -%} {{ predicate }}
+    {% endfor %}
+    );
+
+    {%- set dest_cols_csv = get_quoted_csv(dest_columns | map(attribute="name")) -%}
+    insert into {{ target }} ({{ dest_cols_csv }})
+    (
+        select {{ dest_cols_csv }}
+        from {{ source }}
+    )
+{% endmacro %}

tests/functional/adapter/incremental/test_incremental_microbatch.py

@@ -0,0 +1,24 @@
+import pytest
+from dbt.tests.adapter.incremental.test_incremental_microbatch import (
+    BaseMicrobatch,
+)
+
+
+# No requirement for a unique_id for redshift microbatch!
+_microbatch_model_no_unique_id_sql = """
+{{ config(materialized='incremental', incremental_strategy='microbatch', event_time='event_time', batch_size='day') }}
+select * from {{ ref('input_model') }}
+"""
+
+
+class TestSnowflakeMicrobatch(BaseMicrobatch):
+    @pytest.fixture(scope="class")
+    def microbatch_model_sql(self) -> str:
+        return _microbatch_model_no_unique_id_sql
+
+    @pytest.fixture(scope="class")
+    def insert_two_rows_sql(self, project) -> str:
+        test_schema_relation = project.adapter.Relation.create(
+            database=project.database, schema=project.test_schema
+        )
+        return f"insert into {test_schema_relation}.input_model (id, event_time) values (4, '2020-01-04 00:00:00-0'), (5, '2020-01-05 00:00:00-0')"