From 50f0638fa9ce163ca7a62d8711b440ca29df2688 Mon Sep 17 00:00:00 2001
From: Peter Debelak <pdebelak@gmail.com>
Date: Sat, 9 Jul 2022 15:57:15 -0500
Subject: [PATCH] Allow no alias for selects in CTEs with a column list (#3580)

In cases where the CTE has a column list, we don't need an alias for
columns. This checks if the select has a `common_table_expression`
parent and if that parent has a `cte_column_list` child. In that case,
it doesn't complain about a missing alias.

Fixes #3558
---
 src/sqlfluff/rules/L013.py                  | 15 +++++++++--
 test/fixtures/rules/std_rule_cases/L013.yml | 30 +++++++++++++++++++++
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/src/sqlfluff/rules/L013.py b/src/sqlfluff/rules/L013.py
index d6f2275af9e..4941944316f 100644
--- a/src/sqlfluff/rules/L013.py
+++ b/src/sqlfluff/rules/L013.py
@@ -48,7 +48,8 @@ def _eval(self, context: RuleContext) -> Optional[LintResult]:
         elements there are.
 
         """
-        segment = context.functional.segment
+        functional_context = context.functional
+        segment = functional_context.segment
         children = segment.children()
         # If we have an alias its all good
         if children.any(sp.is_type("alias_expression")):
@@ -66,6 +67,16 @@ def _eval(self, context: RuleContext) -> Optional[LintResult]:
         ):
             return None
 
+        parent_stack = functional_context.parent_stack
+
+        # Ignore if it is part of a CTE with column names
+        if (
+            parent_stack.last(sp.is_type("common_table_expression"))
+            .children()
+            .any(sp.is_type("cte_column_list"))
+        ):
+            return None
+
         select_clause_children = children.select(sp.not_(sp.is_name("star")))
         is_complex_clause = _recursively_check_is_complex(select_clause_children)
         if not is_complex_clause:
@@ -76,7 +87,7 @@ def _eval(self, context: RuleContext) -> Optional[LintResult]:
             # Check *how many* elements/columns there are in the select
             # statement. If this is the only one, then we won't
             # report an error.
-            immediate_parent = context.functional.parent_stack.last()
+            immediate_parent = parent_stack.last()
             elements = immediate_parent.children(sp.is_type("select_clause_element"))
             num_elements = len(elements)
 
diff --git a/test/fixtures/rules/std_rule_cases/L013.yml b/test/fixtures/rules/std_rule_cases/L013.yml
index 4662e4cc9d4..3c245573429 100644
--- a/test/fixtures/rules/std_rule_cases/L013.yml
+++ b/test/fixtures/rules/std_rule_cases/L013.yml
@@ -47,3 +47,33 @@ test_pass_function_emits:
   configs:
     core:
       dialect: exasol
+
+test_fail_cte_no_column_list:
+  fail_str: |
+    WITH cte AS (
+        SELECT
+            col_a,
+            min(col_b)
+        FROM my_table
+        GROUP BY 1
+    )
+
+    SELECT
+        a,
+        b
+    FROM cte
+
+test_pass_cte_column_list:
+  pass_str: |
+    WITH cte(a, b) AS (
+        SELECT
+            col_a,
+            min(col_b)
+        FROM my_table
+        GROUP BY 1
+    )
+
+    SELECT
+        a,
+        b
+    FROM cte