Have union_relations raise exception when include parameter results i…

…n no columns (#473)

* Raise exception if no columns in column_superset

* Add relation names to compiler error message

* Add `union_relations` fix to changelog

CHANGELOG.md

@@ -4,7 +4,11 @@
 - also ignore `dbt_packages/` directory [#463](https://github.com/dbt-labs/dbt-utils/pull/463)
 
 ## Fixes
-- `type_timestamp` macro now explicitly casts postgres and redshift warehouse timestamp data types as `timestamp without time zone`, to be consistent with Snowflake behaviour (`timestamp_ntz`). 
+- `type_timestamp` macro now explicitly casts postgres and redshift warehouse timestamp data types as `timestamp without time zone`, to be consistent with Snowflake behaviour (`timestamp_ntz`).
+- `union_relations` macro will now raise an exception if the use of `include` or `exclude` results in no columns ([#473](https://github.com/dbt-labs/dbt-utils/pull/473), [#266](https://github.com/dbt-labs/dbt-utils/issues/266)).
+
+## Contributors:
+- [grahamwetzler](https://github.com/grahamwetzler) (#473)
 
 # dbt-utils v0.8.0
 ## 🚨 Breaking changes

macros/sql/union.sql

@@ -61,6 +61,21 @@
 
     {%- set ordered_column_names = column_superset.keys() -%}
 
+    {%- if not column_superset.keys() -%}
+        {%- set relations_string -%}
+            {%- for relation in relations -%}
+                {{ relation.name }}
+            {%- if not loop.last %}, {% endif -%}
+            {%- endfor -%}
+        {%- endset -%}
+
+        {%- set error_message -%}
+            There were no columns found to union for relations {{ relations_string }}
+        {%- endset -%}
+
+        {{ exceptions.raise_compiler_error(error_message) }}
+    {%- endif -%}
+
     {%- for relation in relations %}
 
         (