Issue 488 snapshot tmp table

.changes/unreleased/Fixes-20250611-140823.yaml

@@ -0,0 +1,7 @@
+kind: Fixes
+body: Snapshot staging table is recreated every time
+time: 2025-06-11T14:08:23.526502764+02:00
+custom:
+    Author: adam-tokarski
+    Issue: "488"
+    PR: "489"

dbt/include/trino/macros/materializations/snapshot.sql

@@ -48,3 +48,25 @@
             {%- endfor %})
 
 {% endmacro %}
+
+/*
+    Overridden macro which builds a staging table for snapshot.
+
+    As there is no such thing as a temporary table in Trino, such staging table is removed
+    on cleanup (see trino__post_snapshot macro above). But it may happen that something goes
+    wrong (like in `merge` statement), dbt fails and this 'temporary' table still exists.
+    This macro takes care of it.
+ */
+{% macro build_snapshot_staging_table(strategy, sql, target_relation) %}
+    {% set temp_relation = make_temp_relation(target_relation) %}
+
+    {{ drop_relation_if_exists(temp_relation) }}
+
+    {% set select = snapshot_staging_table(strategy, sql, target_relation) %}
+
+    {% call statement('build_snapshot_staging_relation') %}
+        {{ create_table_as(True, temp_relation, select) }}
+    {% endcall %}
+
+    {% do return(temp_relation) %}
+{% endmacro %}

tests/functional/adapter/test_simple_snapshot.py

@@ -3,6 +3,7 @@
     BaseSimpleSnapshot,
     BaseSnapshotCheck,
 )
+from dbt.tests.fixtures.project import TestProjInfo
 from dbt.tests.util import run_dbt
 
 iceberg_macro_override_sql = """
@@ -13,7 +14,7 @@
 
 
 class TrinoSimpleSnapshot(BaseSimpleSnapshot):
-    def test_updates_are_captured_by_snapshot(self, project):
+    def test_updates_are_captured_by_snapshot(self, project: TestProjInfo) -> None:
         """
         Update the last 5 records. Show that all ids are current, but the last 5 reflect updates.
         """
@@ -26,7 +27,7 @@ def test_updates_are_captured_by_snapshot(self, project):
             ids_with_closed_out_snapshot_records=range(16, 21),
         )
 
-    def test_new_column_captured_by_snapshot(self, project):
+    def test_new_column_captured_by_snapshot(self, project: TestProjInfo) -> None:
         """
         Add a column to `fact` and populate the last 10 records with a non-null value.
         Show that all ids are current, but the last 10 reflect updates and the first 10 don't
@@ -47,8 +48,20 @@ def test_new_column_captured_by_snapshot(self, project):
         )
 
 
+    def test_staging_table_is_recreated(self, project: TestProjInfo) -> None:
+        """
+        It may happen that staging temporary table still exists, from previous run.
+        Snapshot should work properly even in such situation.
+        """
+
+        project.run_sql(f"create table {project.test_schema}.snapshot__dbt_tmp (id int)")
+
+        run_dbt(["snapshot"])
+
+
+
 class TrinoSnapshotCheck(BaseSnapshotCheck):
-    def test_column_selection_is_reflected_in_snapshot(self, project):
+    def test_column_selection_is_reflected_in_snapshot(self, project: TestProjInfo) -> None:
         """
         Update the first 10 records on a non-tracked column.
         Update the middle 10 records on a tracked column. (hence records 6-10 are updated on both)