Output '*' in union_relations when no columns are found in compile mode

CHANGELOG.md

@@ -1,8 +1,14 @@
 # Unreleased
 
-**Full Changelog**: https://github.com/dbt-labs/dbt-utils/compare/1.2.0...main
+# dbt utils v1.4.0
+**Full Changelog**: https://github.com/dbt-labs/dbt-utils/compare/1.4.0...main
+* union_relations macro now outputs '*' in compile mode when the upstream relations haven't been built, such as when running SQLFluff on new models
+
+## New Contributors
+* @martinshjung made their first contribution in https://github.com/dbt-labs/dbt-utils/pull/832
 
 # dbt utils v1.2.0
+**Full Changelog**: https://github.com/dbt-labs/dbt-utils/compare/1.2.0...main
 
 ## What's Changed
 

macros/sql/union.sql

@@ -103,6 +103,12 @@
                 cast({{ dbt.string_literal(relation) }} as {{ dbt.type_string() }}) as {{ source_column_name }},
                 {%- endif %}
 
+                /* No columns from any of the relations.
+                   This star is only output during dbt compile, and exists to keep SQLFluff happy. */
+                {% if dbt_command == 'compile' and ordered_column_names|length == 0 %}
+                    *
+                {% endif %}
+
                 {% for col_name in ordered_column_names -%}
 
                     {%- set col = column_superset[col_name] %}