fix(mssql): support cte in virtual tables (#18567)

* Fix for handling regular CTE queries with MSSQL,#8074

* Moved the get_cte_query function from mssql.py to base.py for using irrespetcive of dbengine

* Fix for handling regular CTE queries with MSSQL,#8074

* Moved the get_cte_query function from mssql.py to base.py for using irrespetcive of dbengine

* Unit test added for the db engine CTE SQL parsing.

Unit test added for the db engine CTE SQL parsing.  Removed additional spaces from the CTE parsing SQL generation.

* implement in sqla model

* lint + cleanup

Co-authored-by: Ville Brofeldt <ville.v.brofeldt@gmail.com>

superset/connectors/sqla/models.py

@@ -77,7 +77,7 @@
     get_physical_table_metadata,
     get_virtual_table_metadata,
 )
-from superset.db_engine_specs.base import BaseEngineSpec, TimestampExpression
+from superset.db_engine_specs.base import BaseEngineSpec, CTE_ALIAS, TimestampExpression
 from superset.exceptions import QueryObjectValidationError
 from superset.jinja_context import (
     BaseTemplateProcessor,
@@ -107,6 +107,7 @@
 
 class SqlaQuery(NamedTuple):
     applied_template_filters: List[str]
+    cte: Optional[str]
     extra_cache_keys: List[Any]
     labels_expected: List[str]
     prequeries: List[str]
@@ -562,6 +563,19 @@ class SqlaTable(Model, BaseDatasource):  # pylint: disable=too-many-public-metho
     def __repr__(self) -> str:
         return self.name
 
+    @staticmethod
+    def _apply_cte(sql: str, cte: Optional[str]) -> str:
+        """
+        Append a CTE before the SELECT statement if defined
+
+        :param sql: SELECT statement
+        :param cte: CTE statement
+        :return:
+        """
+        if cte:
+            sql = f"{cte}\n{sql}"
+        return sql
+
     @property
     def db_engine_spec(self) -> Type[BaseEngineSpec]:
         return self.database.db_engine_spec
@@ -743,20 +757,18 @@ def values_for_column(self, column_name: str, limit: int = 10000) -> List[Any]:
         cols = {col.column_name: col for col in self.columns}
         target_col = cols[column_name]
         tp = self.get_template_processor()
+        tbl, cte = self.get_from_clause(tp)
 
-        qry = (
-            select([target_col.get_sqla_col()])
-            .select_from(self.get_from_clause(tp))
-            .distinct()
-        )
+        qry = select([target_col.get_sqla_col()]).select_from(tbl).distinct()
         if limit:
             qry = qry.limit(limit)
 
         if self.fetch_values_predicate:
             qry = qry.where(self.get_fetch_values_predicate())
 
         engine = self.database.get_sqla_engine()
-        sql = "{}".format(qry.compile(engine, compile_kwargs={"literal_binds": True}))
+        sql = qry.compile(engine, compile_kwargs={"literal_binds": True})
+        sql = self._apply_cte(sql, cte)
         sql = self.mutate_query_from_config(sql)
 
         df = pd.read_sql_query(sql=sql, con=engine)
@@ -778,6 +790,7 @@ def get_template_processor(self, **kwargs: Any) -> BaseTemplateProcessor:
     def get_query_str_extended(self, query_obj: QueryObjectDict) -> QueryStringExtended:
         sqlaq = self.get_sqla_query(**query_obj)
         sql = self.database.compile_sqla_query(sqlaq.sqla_query)
+        sql = self._apply_cte(sql, sqlaq.cte)
         sql = sqlparse.format(sql, reindent=True)
         sql = self.mutate_query_from_config(sql)
         return QueryStringExtended(
@@ -800,13 +813,14 @@ def get_sqla_table(self) -> TableClause:
 
     def get_from_clause(
         self, template_processor: Optional[BaseTemplateProcessor] = None
-    ) -> Union[TableClause, Alias]:
+    ) -> Tuple[Union[TableClause, Alias], Optional[str]]:
         """
         Return where to select the columns and metrics from. Either a physical table
-        or a virtual table with it's own subquery.
+        or a virtual table with it's own subquery. If the FROM is referencing a
+        CTE, the CTE is returned as the second value in the return tuple.
         """
         if not self.is_virtual:
-            return self.get_sqla_table()
+            return self.get_sqla_table(), None
 
         from_sql = self.get_rendered_sql(template_processor)
         parsed_query = ParsedQuery(from_sql)
@@ -817,7 +831,15 @@ def get_from_clause(
             raise QueryObjectValidationError(
                 _("Virtual dataset query must be read-only")
             )
-        return TextAsFrom(self.text(from_sql), []).alias(VIRTUAL_TABLE_ALIAS)
+
+        cte = self.db_engine_spec.get_cte_query(from_sql)
+        from_clause = (
+            table(CTE_ALIAS)
+            if cte
+            else TextAsFrom(self.text(from_sql), []).alias(VIRTUAL_TABLE_ALIAS)
+        )
+
+        return from_clause, cte
 
     def get_rendered_sql(
         self, template_processor: Optional[BaseTemplateProcessor] = None
@@ -1224,7 +1246,7 @@ def get_sqla_query(  # pylint: disable=too-many-arguments,too-many-locals,too-ma
 
         qry = sa.select(select_exprs)
 
-        tbl = self.get_from_clause(template_processor)
+        tbl, cte = self.get_from_clause(template_processor)
 
         if groupby_all_columns:
             qry = qry.group_by(*groupby_all_columns.values())
@@ -1491,6 +1513,7 @@ def get_sqla_query(  # pylint: disable=too-many-arguments,too-many-locals,too-ma
 
         return SqlaQuery(
             applied_template_filters=applied_template_filters,
+            cte=cte,
             extra_cache_keys=extra_cache_keys,
             labels_expected=labels_expected,
             sqla_query=qry,

superset/db_engine_specs/base.py

@@ -54,6 +54,7 @@
 from sqlalchemy.sql import quoted_name, text
 from sqlalchemy.sql.expression import ColumnClause, Select, TextAsFrom, TextClause
 from sqlalchemy.types import TypeEngine
+from sqlparse.tokens import CTE
 from typing_extensions import TypedDict
 
 from superset import security_manager, sql_parse
@@ -80,6 +81,9 @@
 logger = logging.getLogger()
 
 
+CTE_ALIAS = "__cte"
+
+
 class TimeGrain(NamedTuple):
     name: str  # TODO: redundant field, remove
     label: str
@@ -292,6 +296,11 @@ class BaseEngineSpec:  # pylint: disable=too-many-public-methods
     # But for backward compatibility, False by default
     allows_hidden_cc_in_orderby = False
 
+    # Whether allow CTE as subquery or regular CTE
+    # If True, then it will allow  in subquery ,
+    # if False it will allow as regular CTE
+    allows_cte_in_subquery = True
+
     force_column_alias_quotes = False
     arraysize = 0
     max_column_name_length = 0
@@ -663,6 +672,31 @@ def set_or_update_query_limit(cls, sql: str, limit: int) -> str:
         parsed_query = sql_parse.ParsedQuery(sql)
         return parsed_query.set_or_update_query_limit(limit)
 
+    @classmethod
+    def get_cte_query(cls, sql: str) -> Optional[str]:
+        """
+        Convert the input CTE based SQL to the SQL for virtual table conversion
+
+        :param sql: SQL query
+        :return: CTE with the main select query aliased as `__cte`
+
+        """
+        if not cls.allows_cte_in_subquery:
+            stmt = sqlparse.parse(sql)[0]
+
+            # The first meaningful token for CTE will be with WITH
+            idx, token = stmt.token_next(-1, skip_ws=True, skip_cm=True)
+            if not (token and token.ttype == CTE):
+                return None
+            idx, token = stmt.token_next(idx)
+            idx = stmt.token_index(token) + 1
+
+            # extract rest of the SQLs after CTE
+            remainder = "".join(str(token) for token in stmt.tokens[idx:]).strip()
+            return f"WITH {token.value},\n{CTE_ALIAS} AS (\n{remainder}\n)"
+
+        return None
+
     @classmethod
     def df_to_sql(
         cls,

superset/db_engine_specs/mssql.py

@@ -47,6 +47,7 @@ class MssqlEngineSpec(BaseEngineSpec):
     engine_name = "Microsoft SQL Server"
     limit_method = LimitMethod.WRAP_SQL
     max_column_name_length = 128
+    allows_cte_in_subquery = False
 
     _time_grain_expressions = {
         None: "{col}",

tests/integration_tests/core_tests.py

@@ -984,7 +984,7 @@ def test_comments_in_sqlatable_query(self):
             sql=commented_query,
             database=get_example_database(),
         )
-        rendered_query = str(table.get_from_clause())
+        rendered_query = str(table.get_from_clause()[0])
         self.assertEqual(clean_query, rendered_query)
 
     def test_slice_payload_no_datasource(self):

tests/unit_tests/db_engine_specs/test_base.py

@@ -16,7 +16,11 @@
 # under the License.
 # pylint: disable=unused-argument, import-outside-toplevel, protected-access
 
+from textwrap import dedent
+
+import pytest
 from flask.ctx import AppContext
+from sqlalchemy.types import TypeEngine
 
 
 def test_get_text_clause_with_colon(app_context: AppContext) -> None:
@@ -56,3 +60,42 @@ def test_parse_sql_multi_statement(app_context: AppContext) -> None:
         "SELECT foo FROM tbl1",
         "SELECT bar FROM tbl2",
     ]
+
+
+@pytest.mark.parametrize(
+    "original,expected",
+    [
+        (
+            dedent(
+                """
+with currency as
+(
+select 'INR' as cur
+)
+select * from currency
+"""
+            ),
+            None,
+        ),
+        ("SELECT 1 as cnt", None,),
+        (
+            dedent(
+                """
+select 'INR' as cur
+union
+select 'AUD' as cur
+union
+select 'USD' as cur
+"""
+            ),
+            None,
+        ),
+    ],
+)
+def test_cte_query_parsing(
+    app_context: AppContext, original: TypeEngine, expected: str
+) -> None:
+    from superset.db_engine_specs.base import BaseEngineSpec
+
+    actual = BaseEngineSpec.get_cte_query(original)
+    assert actual == expected

tests/unit_tests/db_engine_specs/test_mssql.py

@@ -180,6 +180,57 @@ def test_column_datatype_to_string(
     assert actual == expected
 
 
+@pytest.mark.parametrize(
+    "original,expected",
+    [
+        (
+            dedent(
+                """
+with currency as (
+select 'INR' as cur
+),
+currency_2 as (
+select 'EUR' as cur
+)
+select * from currency union all select * from currency_2
+"""
+            ),
+            dedent(
+                """WITH currency as (
+select 'INR' as cur
+),
+currency_2 as (
+select 'EUR' as cur
+),
+__cte AS (
+select * from currency union all select * from currency_2
+)"""
+            ),
+        ),
+        ("SELECT 1 as cnt", None,),
+        (
+            dedent(
+                """
+select 'INR' as cur
+union
+select 'AUD' as cur
+union
+select 'USD' as cur
+"""
+            ),
+            None,
+        ),
+    ],
+)
+def test_cte_query_parsing(
+    app_context: AppContext, original: TypeEngine, expected: str
+) -> None:
+    from superset.db_engine_specs.mssql import MssqlEngineSpec
+
+    actual = MssqlEngineSpec.get_cte_query(original)
+    assert actual == expected
+
+
 def test_extract_errors(app_context: AppContext) -> None:
     """
     Test that custom error messages are extracted correctly.