fix: avoid aliasing known tables used in CTEs (#369)

Toward #368.

Author: tseaver

Diff for: sqlalchemy_bigquery/base.py

@@ -51,6 +51,7 @@
 from sqlalchemy.engine.base import Engine
 from sqlalchemy.sql.schema import Column
 from sqlalchemy.sql.schema import Table
+from sqlalchemy.sql.selectable import CTE
 from sqlalchemy.sql import elements, selectable
 import re
 
@@ -254,6 +255,20 @@ def visit_table_valued_alias(self, element, **kw):
             ret = f"{aliases}, {ret}"
         return ret
 
+    def _known_tables(self):
+        known_tables = set()
+
+        for from_ in self.compile_state.froms:
+            if isinstance(from_, Table):
+                known_tables.add(from_.name)
+            elif isinstance(from_, CTE):
+                for column in from_.original.selected_columns:
+                    table = getattr(column, "table", None)
+                    if table is not None:
+                        known_tables.add(table.name)
+
+        return known_tables
+
     def visit_column(
         self,
         column,
@@ -290,12 +305,7 @@ def visit_column(
             if isinstance(tablename, elements._truncated_label):
                 tablename = self._truncated_identifier("alias", tablename)
             elif TABLE_VALUED_ALIAS_ALIASES in kwargs:
-                known_tables = set(
-                    from_.name
-                    for from_ in self.compile_state.froms
-                    if isinstance(from_, Table)
-                )
-                if tablename not in known_tables:
+                if tablename not in self._known_tables():
                     aliases = kwargs[TABLE_VALUED_ALIAS_ALIASES]
                     if tablename not in aliases:
                         aliases[tablename] = self.anon_map[

Diff for: tests/unit/test_compiler.py

@@ -76,3 +76,39 @@ def test_no_alias_for_known_tables(faux_conn, metadata):
     )
     found_sql = q.compile(faux_conn).string
     assert found_sql == expected_sql
+
+
+@sqlalchemy_1_4_or_higher
+def test_no_alias_for_known_tables_cte(faux_conn, metadata):
+    # See: https://github.com/googleapis/python-bigquery-sqlalchemy/issues/368
+    table = setup_table(
+        faux_conn,
+        "table1",
+        metadata,
+        sqlalchemy.Column("foo", sqlalchemy.Integer),
+        sqlalchemy.Column("bars", sqlalchemy.ARRAY(sqlalchemy.Integer)),
+    )
+    F = sqlalchemy.func
+
+    # Set up initiali query
+    q = sqlalchemy.select(table.c.foo, F.unnest(table.c.bars).column_valued("bar"))
+
+    expected_initial_sql = (
+        "SELECT `table1`.`foo`, `bar` \n"
+        "FROM `table1`, unnest(`table1`.`bars`) AS `bar`"
+    )
+    found_initial_sql = q.compile(faux_conn).string
+    assert found_initial_sql == expected_initial_sql
+
+    q = q.cte("cte")
+    q = sqlalchemy.select(*q.columns)
+
+    expected_cte_sql = (
+        "WITH `cte` AS \n"
+        "(SELECT `table1`.`foo` AS `foo`, `bar` \n"
+        "FROM `table1`, unnest(`table1`.`bars`) AS `bar`)\n"
+        " SELECT `cte`.`foo`, `cte`.`bar` \n"
+        "FROM `cte`"
+    )
+    found_cte_sql = q.compile(faux_conn).string
+    assert found_cte_sql == expected_cte_sql