Empty unit test fixtures (rows: []) emit invalid LIMIT 0 syntax

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+### v1.10.1
+
+#### Bugfixes
+
+- Fix unit tests with empty fixtures (`rows: []`) generating invalid `limit 0` syntax; emit `top 0` instead. Also fix `get_columns_in_query()` for queries starting with a CTE, which broke unit tests with an empty `expect` block; such queries are now described via `sp_describe_first_result_set` instead of being executed. [#698](https://github.com/dbt-msft/dbt-sqlserver/issues/698)
+
 ### v1.10.0
 
 #### Features

dbt/include/sqlserver/macros/adapters/columns.sql

@@ -1,6 +1,11 @@
-{% macro sqlserver__get_empty_subquery_sql(select_sql, select_sql_header=none) %}
+{% macro sqlserver__select_starts_with_cte(select_sql) %}
+    {#-- Strip comments first so a leading comment does not hide the CTE --#}
     {%- set select_sql_stripped = modules.re.sub('(?s)/\\*.*?\\*/|--[^\n]*\n', '', select_sql) -%}
-    {% if select_sql_stripped.strip().lower().startswith('with') %}
+    {{ return(select_sql_stripped.strip().lower().startswith('with')) }}
+{% endmacro %}
+
+{% macro sqlserver__get_empty_subquery_sql(select_sql, select_sql_header=none) %}
+    {% if sqlserver__select_starts_with_cte(select_sql) %}
         {{ select_sql }}
     {% else -%}
         select * from (
@@ -13,15 +18,22 @@
 
 {% macro sqlserver__get_columns_in_query(select_sql) %}
     {% set query_label = get_query_options() %}
-    {% call statement('get_columns_in_query', fetch_result=True, auto_begin=False) -%}
-        select TOP 0 * from (
-            {{ select_sql }}
-        ) as __dbt_sbq
-        where 0 = 1
-        {{ query_label }}
-    {% endcall %}
-
-    {{ return(load_result('get_columns_in_query').table.columns | map(attribute='name') | list) }}
+    {% if sqlserver__select_starts_with_cte(select_sql) %}
+        {#-- A query starting with a CTE cannot be wrapped in a subquery; describe its result set instead of executing it (dbt-msft/dbt-sqlserver#698) --#}
+        {% call statement('get_columns_in_query', fetch_result=True, auto_begin=False) -%}
+            exec sp_describe_first_result_set @tsql = N'{{ escape_single_quotes(select_sql) }}'
+        {% endcall %}
+        {{ return(load_result('get_columns_in_query').table.columns['name'].values() | list) }}
+    {% else %}
+        {% call statement('get_columns_in_query', fetch_result=True, auto_begin=False) -%}
+            select TOP 0 * from (
+                {{ select_sql }}
+            ) as __dbt_sbq
+            where 0 = 1
+            {{ query_label }}
+        {% endcall %}
+        {{ return(load_result('get_columns_in_query').table.columns | map(attribute='name') | list) }}
+    {% endif %}
 {% endmacro %}
 
 {% macro sqlserver__alter_column_type(relation, column_name, new_column_type) %}

dbt/include/sqlserver/macros/materializations/models/unit_test/get_fixture_sql.sql

@@ -0,0 +1,83 @@
+{#
+    dbt-core does not dispatch "get_fixture_sql" or "get_expected_sql", so this file
+    shadows the implementations from the dbt global project
+    (macros/unit_test_sql/get_fixture_sql.sql) - adapter package macros take
+    precedence over the global project. Keep in sync with dbt-core when upgrading.
+
+    Changes from upstream (see dbt-msft/dbt-sqlserver#698):
+      - get_fixture_sql: the empty-rows branch emits "select top 0" instead of
+        "limit 0", which is not valid T-SQL.
+      - get_expected_sql: the empty-rows branch emits a "select top 0" of typed
+        nulls instead of "select * from dbt_internal_unit_test_actual limit 0".
+        Besides the invalid "limit", sqlserver__get_unit_test_sql wraps the
+        expected SQL in its own view, where that CTE name is out of scope.
+#}
+
+{% macro get_fixture_sql(rows, column_name_to_data_types) %}
+-- Fixture for {{ model.name }}
+{% set default_row = {} %}
+
+{%- if not column_name_to_data_types -%}
+{#-- Use defer_relation IFF it is available in the manifest and 'this' is missing from the database --#}
+{%-   set this_or_defer_relation = defer_relation if (defer_relation and not load_relation(this)) else this -%}
+{%-   set columns_in_relation = adapter.get_columns_in_relation(this_or_defer_relation) -%}
+
+{%-   set column_name_to_data_types = {} -%}
+{%-   set column_name_to_quoted = {} -%}
+{%-   for column in columns_in_relation -%}
+
+{#-- This needs to be a case-insensitive comparison --#}
+{%-     do column_name_to_data_types.update({column.name|lower: column.data_type}) -%}
+{%-     do column_name_to_quoted.update({column.name|lower: column.quoted}) -%}
+{%-   endfor -%}
+{%- endif -%}
+
+{%- if not column_name_to_data_types -%}
+    {{ exceptions.raise_compiler_error("Not able to get columns for unit test '" ~ model.name ~ "' from relation " ~ this ~ " because the relation doesn't exist") }}
+{%- endif -%}
+
+{%- for column_name, column_type in column_name_to_data_types.items() -%}
+    {%- do default_row.update({column_name: (safe_cast("null", column_type) | trim )}) -%}
+{%- endfor -%}
+
+{{ validate_fixture_rows(rows, row_number) }}
+
+{%- for row in rows -%}
+{%-   set formatted_row = format_row(row, column_name_to_data_types) -%}
+{%-   set default_row_copy = default_row.copy() -%}
+{%-   do default_row_copy.update(formatted_row) -%}
+select
+{%-   for column_name, column_value in default_row_copy.items() %} {{ column_value }} as {{ column_name_to_quoted[column_name] }}{% if not loop.last -%}, {%- endif %}
+{%-   endfor %}
+{%-   if not loop.last %}
+union all
+{%    endif %}
+{%- endfor -%}
+
+{%- if (rows | length) == 0 -%}
+    select top 0
+    {%- for column_name, column_value in default_row.items() %} {{ column_value }} as {{ column_name_to_quoted[column_name] }}{% if not loop.last -%},{%- endif %}
+    {%- endfor %}
+{%- endif -%}
+{% endmacro %}
+
+
+{% macro get_expected_sql(rows, column_name_to_data_types, column_name_to_quoted) %}
+
+{%- if (rows | length) == 0 -%}
+    select top 0
+    {%- for column_name, column_type in column_name_to_data_types.items() %} {{ safe_cast("null", column_type) | trim }} as {{ column_name_to_quoted[column_name] }}{% if not loop.last -%},{%- endif %}
+    {%- endfor %}
+{%- else -%}
+{%- for row in rows -%}
+{%- set formatted_row = format_row(row, column_name_to_data_types) -%}
+select
+{%- for column_name, column_value in formatted_row.items() %} {{ column_value }} as {{ column_name_to_quoted[column_name] }}{% if not loop.last -%}, {%- endif %}
+{%- endfor %}
+{%- if not loop.last %}
+union all
+{% endif %}
+{%- endfor -%}
+{%- endif -%}
+
+{% endmacro %}

tests/functional/adapter/dbt/test_unit_tests.py

@@ -28,6 +28,41 @@
         - {{ tested_column: {yaml_value} }}
 """
 
+my_union_model_sql = """
+select tested_column from {{ ref('my_upstream_model') }}
+union all
+select tested_column from {{ ref('my_other_upstream_model') }}
+"""
+
+upstream_model_sql = """
+select 1 as tested_column
+"""
+
+# `rows: []` must not generate `limit 0`, which is invalid T-SQL (issue #698)
+test_empty_fixture_yml = """
+unit_tests:
+  - name: test_empty_given
+    model: my_union_model
+    given:
+      - input: ref('my_upstream_model')
+        rows:
+          - {tested_column: 1}
+      - input: ref('my_other_upstream_model')
+        rows: []
+    expect:
+      rows:
+        - {tested_column: 1}
+  - name: test_empty_expect
+    model: my_union_model
+    given:
+      - input: ref('my_upstream_model')
+        rows: []
+      - input: ref('my_other_upstream_model')
+        rows: []
+    expect:
+      rows: []
+"""
+
 
 class TestUnitTestCaseInsensitivity(BaseUnitTestCaseInsensivity):
     pass
@@ -37,6 +72,24 @@ class TestUnitTestInvalidInput(BaseUnitTestInvalidInput):
     pass
 
 
+class TestUnitTestEmptyFixture:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "my_upstream_model.sql": upstream_model_sql,
+            "my_other_upstream_model.sql": upstream_model_sql,
+            "my_union_model.sql": my_union_model_sql,
+            "schema.yml": test_empty_fixture_yml,
+        }
+
+    def test_empty_fixture_rows(self, project):
+        results = run_dbt(["run"])
+        assert len(results) == 3
+
+        results = run_dbt(["test", "--select", "my_union_model"])
+        assert len(results) == 2
+
+
 class TestUnitTestingTypes(BaseUnitTestingTypes):
     @pytest.fixture
     def data_types(self):