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new c39a47cbac5 test(sql-parser): pin WITH+UNION as non-mutating across
dialects (#25659) (#40138)
c39a47cbac5 is described below
commit c39a47cbac52bab2f51e38755483b5439dba54c6
Author: Evan Rusackas <[email protected]>
AuthorDate: Wed May 20 10:08:21 2026 -0700
test(sql-parser): pin WITH+UNION as non-mutating across dialects (#25659)
(#40138)
Co-authored-by: Claude Code <[email protected]>
---
tests/unit_tests/sql/parse_tests.py | 45 +++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/tests/unit_tests/sql/parse_tests.py
b/tests/unit_tests/sql/parse_tests.py
index bbf4ec2e527..b6d0c558053 100644
--- a/tests/unit_tests/sql/parse_tests.py
+++ b/tests/unit_tests/sql/parse_tests.py
@@ -1190,6 +1190,51 @@ def test_postgres_parses_timescaledb_hyperfunctions(sql:
str) -> None:
SQLScript(sql, "postgresql") # Must not raise.
[email protected](
+ "engine",
+ ["oracle", "postgresql", "trino", "presto", "hive", "base"],
+)
+def test_with_clause_containing_union_is_not_mutating(engine: str) -> None:
+ """
+ Regression for #25659: a SELECT with a WITH clause whose CTEs contain
+ UNION (or UNION ALL) must not be classified as mutating, on any dialect.
+
+ The original bug surfaced on Oracle, where saving a virtual dataset built
+ from such a query failed with "Only `SELECT` statements are allowed". The
+ parser was misclassifying the WITH+UNION construct as DML.
+
+ Multiple dialects are exercised because the bug arose from sqlglot's
+ per-dialect AST shape — Oracle's representation of the same query may
+ differ from Postgres/Trino, and a fix that only touches one dialect
+ leaves the others exposed to the same regression.
+ """
+ sql = """
+ WITH set1 AS (SELECT 1 AS n UNION SELECT 2),
+ set2 AS (SELECT * FROM set1)
+ SELECT * FROM set2
+ """
+ assert not SQLScript(sql, engine).has_mutation(), (
+ f"WITH+UNION misclassified as mutating on {engine!r}; "
+ "this would block the query from being saved as a virtual dataset."
+ )
+
+
+def test_with_clause_containing_union_all_is_not_mutating_oracle() -> None:
+ """
+ Companion to test_with_clause_containing_union_is_not_mutating: the
+ original bug report (#25659) used the exact Oracle-flavored shape below
+ (``SYSDATE FROM DUAL`` is the Oracle no-op for "now"). Pinning the
+ verbatim repro guards against a future dialect-specific regression that
+ a generic ``SELECT 1`` test might miss.
+ """
+ sql = """
+ WITH SET1 AS (SELECT SYSDATE FROM DUAL UNION ALL SELECT SYSDATE FROM DUAL),
+ SET2 AS (SELECT * FROM SET1)
+ SELECT * FROM SET2
+ """
+ assert not SQLScript(sql, "oracle").has_mutation()
+
+
def test_get_settings() -> None:
"""
Test `get_settings` in some edge cases.
