fix: Forward port fix for schema checking (#1262)

Forward-ported fix from 1.10.15 to 1.11.1.

The previous implementation relied on list_schemas which could be
unreliable. This change introduces a dedicated check_schema_exists macro
that uses SHOW SCHEMAS ... LIKE for precise matching.

Changes:
- Modified check_schema_exists in impl.py to use execute_macro
- Added databricks__check_schema_exists and check_schema_exists_sql
macros
- Added databricks__list_schemas and list_schemas_sql macros
- Added functional test for schema existence checking

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: benc-db

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Fixes
 
 - Fix bug that was applying UniForm tblproperties on managed Iceberg tables causing materializations to fail
+- Switch to a more reliable mechanism for checking schema existence (forward-ported from 1.10.15) ([1261](https://github.com/databricks/dbt-databricks/pull/1261))
 
 ### Under the hood
 

dbt/adapters/databricks/impl.py

@@ -387,9 +387,11 @@ def list_schemas(self, database: Optional[str]) -> list[str]:
 
     def check_schema_exists(self, database: Optional[str], schema: str) -> bool:
         """Check if a schema exists."""
-        return schema.lower() in set(
-            s.lower() for s in self.connections.list_schemas(database or "hive_metastore", schema)
+        results = self.execute_macro(
+            "databricks__check_schema_exists",
+            kwargs={"database": database or "hive_metastore", "schema": schema},
         )
+        return len(results) > 0
 
     def execute(
         self,

dbt/include/databricks/macros/adapters/metadata.sql

@@ -23,9 +23,30 @@ SHOW TABLE EXTENDED IN {{ schema_relation.without_identifier()|lower }} LIKE '{{
 {% endmacro %}
 
 {% macro show_tables_sql(relation) %}
+
 SHOW TABLES IN {{ relation.render() }}
 {% endmacro %}
 
+{% macro databricks__list_schemas(database) -%}
+  {{ return(run_query_as(list_schemas_sql(database), 'list_schemas')) }}
+{% endmacro %}
+
+{% macro list_schemas_sql(database) %}
+{% if database %}
+  SHOW SCHEMAS IN {{ database }}
+{% else %}
+  SHOW SCHEMAS
+{% endif %}
+{% endmacro %}
+
+{% macro databricks__check_schema_exists(database, schema) %}
+  {{ return(run_query_as(check_schema_exists_sql(database, schema), 'check_schema_exists')) }}
+{% endmacro %}
+
+{% macro check_schema_exists_sql(database, schema) %}
+  SHOW SCHEMAS IN {{ database }} LIKE '{{ schema }}'
+{% endmacro %}
+
 {% macro show_views(relation) %}
   {{ return(adapter.dispatch('show_views', 'dbt')(relation)) }}
 {% endmacro %}

tests/functional/adapter/basic/test_check_schema_exists.py

@@ -0,0 +1,57 @@
+import pytest
+
+
+class TestCheckSchemaExists:
+    """Test the check_schema_exists adapter method."""
+
+    @pytest.fixture(scope="class", autouse=True)
+    def setUp(self, project):
+        """Create a test schema and clean it up after tests."""
+        test_schema = f"{project.test_schema}_check_exists"
+
+        with project.adapter.connection_named("__test"):
+            relation = project.adapter.Relation.create(
+                database=project.database,
+                schema=test_schema,
+            )
+            # Drop if exists from previous run
+            project.adapter.drop_schema(relation)
+            # Create the test schema
+            project.adapter.create_schema(relation)
+
+        yield test_schema
+
+        # Cleanup
+        with project.adapter.connection_named("__test"):
+            project.adapter.drop_schema(relation)
+
+    def test_check_schema_exists(self, project, setUp):
+        """Test that check_schema_exists correctly identifies existing and non-existing schemas."""
+        test_schema = setUp
+
+        with project.adapter.connection_named("__test"):
+            # Test 1: Verify existing schema returns True
+            exists = project.adapter.check_schema_exists(
+                database=project.database, schema=test_schema
+            )
+            assert exists is True, (
+                f"Expected schema '{test_schema}' to exist but check returned False"
+            )
+
+            # Test 2: Verify non-existing schema returns False
+            non_existent_schema = "this_schema_definitely_does_not_exist_12345"
+            exists = project.adapter.check_schema_exists(
+                database=project.database, schema=non_existent_schema
+            )
+            assert exists is False, (
+                f"Expected schema '{non_existent_schema}' to not exist but check returned True"
+            )
+
+            # Test 3: Verify existing default schema returns True (should always exist)
+            exists = project.adapter.check_schema_exists(
+                database=project.database, schema=project.test_schema
+            )
+            assert exists is True, (
+                f"Expected default test schema '{project.test_schema}' "
+                "to exist but check returned False"
+            )