Make aliasing subquery configurable for render_limited (#179)

.changes/unreleased/Features-20240418-155123.yaml

@@ -0,0 +1,6 @@
+kind: Features
+body: Allow adapters to opt out of aliasing the subquery generated by render_limited
+time: 2024-04-18T15:51:23.584295-07:00
+custom:
+  Author: colin-rogers-dbt
+  Issue: "124"

.changes/unreleased/Features-20240418-155531.yaml

@@ -0,0 +1,7 @@
+kind: Features
+body: subquery alias generated by render_limited now includes the relation name to
+  mitigate duplicate aliasing
+time: 2024-04-18T15:55:31.826729-07:00
+custom:
+  Author: colin-rogers-dbt
+  Issue: ' 124'

dbt-tests-adapter/dbt/tests/adapter/empty/test_empty.py

@@ -72,5 +72,24 @@ def test_run_with_empty(self, project):
         self.assert_row_count(project, "model", 0)
 
 
+class BaseTestEmptyInlineSourceRef(BaseTestEmpty):
+    @pytest.fixture(scope="class")
+    def models(self):
+        model_sql = """
+            select * from {{ source('seed_sources', 'raw_source') }} as raw_source
+            """
+
+        return {
+            "model.sql": model_sql,
+            "sources.yml": schema_sources_yml,
+        }
+
+    def test_run_with_empty(self, project):
+        # create source from seed
+        run_dbt(["seed"])
+        run_dbt(["run", "--empty", "--debug"])
+        self.assert_row_count(project, "model", 0)
+
+
 class TestEmpty(BaseTestEmpty):
     pass

dbt/adapters/base/relation.py

@@ -47,6 +47,9 @@ class BaseRelation(FakeAPIObject, Hashable):
     quote_policy: Policy = field(default_factory=lambda: Policy())
     dbt_created: bool = False
     limit: Optional[int] = None
+    require_alias: bool = (
+        True  # used to govern whether to add an alias when render_limited is called
+    )
 
     # register relation types that can be renamed for the purpose of replacing relations using stages and backups
     # adding a relation type here also requires defining the associated rename macro
@@ -205,14 +208,22 @@ def render(self) -> str:
         # if there is nothing set, this will return the empty string.
         return ".".join(part for _, part in self._render_iterator() if part is not None)
 
+    def _render_limited_alias(self) -> str:
+        """Some databases require an alias for subqueries (postgres, mysql) for all others we want to avoid adding
+        an alias as it has the potential to introduce issues with the query if the user also defines an alias.
+        """
+        if self.require_alias:
+            return f" _dbt_limit_subq_{self.table}"
+        return ""
+
     def render_limited(self) -> str:
         rendered = self.render()
         if self.limit is None:
             return rendered
         elif self.limit == 0:
-            return f"(select * from {rendered} where false limit 0) _dbt_limit_subq"
+            return f"(select * from {rendered} where false limit 0){self._render_limited_alias()}"
         else:
-            return f"(select * from {rendered} limit {self.limit}) _dbt_limit_subq"
+            return f"(select * from {rendered} limit {self.limit}){self._render_limited_alias()}"
 
     def quoted(self, identifier):
         return "{quote_char}{identifier}{quote_char}".format(

tests/unit/test_relation.py

@@ -43,25 +43,38 @@ def test_can_be_replaced_default():
 
 
 @pytest.mark.parametrize(
-    "limit,expected_result",
+    "limit,require_alias,expected_result",
     [
-        (None, '"test_database"."test_schema"."test_identifier"'),
+        (None, False, '"test_database"."test_schema"."test_identifier"'),
         (
             0,
-            '(select * from "test_database"."test_schema"."test_identifier" where false limit 0) _dbt_limit_subq',
+            True,
+            '(select * from "test_database"."test_schema"."test_identifier" where false limit 0) _dbt_limit_subq_test_identifier',
         ),
         (
             1,
-            '(select * from "test_database"."test_schema"."test_identifier" limit 1) _dbt_limit_subq',
+            True,
+            '(select * from "test_database"."test_schema"."test_identifier" limit 1) _dbt_limit_subq_test_identifier',
+        ),
+        (
+            0,
+            False,
+            '(select * from "test_database"."test_schema"."test_identifier" where false limit 0)',
+        ),
+        (
+            1,
+            False,
+            '(select * from "test_database"."test_schema"."test_identifier" limit 1)',
         ),
     ],
 )
-def test_render_limited(limit, expected_result):
+def test_render_limited(limit, require_alias, expected_result):
     my_relation = BaseRelation.create(
         database="test_database",
         schema="test_schema",
         identifier="test_identifier",
         limit=limit,
+        require_alias=require_alias,
     )
     actual_result = my_relation.render_limited()
     assert actual_result == expected_result