Ensure subqueries used as CASE targets are not aliased.

Fixes #2905

peewee.py

@@ -1827,6 +1827,16 @@ def __sql__(self, ctx):
         return ctx.literal(self.window._alias or 'w')
 
 
+class _InFunction(Node):
+    def __init__(self, node, in_function=True):
+        self.node = node
+        self.in_function = in_function
+
+    def __sql__(self, ctx):
+        with ctx(in_function=self.in_function):
+            return ctx.sql(self.node)
+
+
 class Case(ColumnBase):
     def __init__(self, predicate, expression_tuples, default=None):
         self.predicate = predicate
@@ -1838,9 +1848,10 @@ def __sql__(self, ctx):
         if self.predicate is not None:
             clauses.append(self.predicate)
         for expr, value in self.expression_tuples:
-            clauses.extend((SQL('WHEN'), expr, SQL('THEN'), value))
+            clauses.extend((SQL('WHEN'), expr,
+                            SQL('THEN'), _InFunction(value)))
         if self.default is not None:
-            clauses.extend((SQL('ELSE'), self.default))
+            clauses.extend((SQL('ELSE'), _InFunction(self.default)))
         clauses.append(SQL('END'))
         with ctx(in_function=False):
             return ctx.sql(NodeList(clauses))

tests/sql.py

@@ -1802,6 +1802,20 @@ def test_case_subquery(self):
             'CASE WHEN ("t1"."id" IN (SELECT "t1"."id" FROM "n" AS "t1")) '
             'THEN ? ELSE ? END) FROM "n" AS "t1"'), [1, 0])
 
+        case = Case(None, [
+            (Name.id < 5, Name.select(fn.SUM(Name.id))),
+            (Name.id > 5, Name.select(fn.COUNT(Name.name)).distinct())],
+            Name.select(fn.MAX(Name.id)))
+        q = Name.select(Name.name, case.alias('magic'))
+        self.assertSQL(q, (
+            'SELECT "t1"."name", CASE '
+            'WHEN ("t1"."id" < ?) '
+            'THEN (SELECT SUM("t1"."id") FROM "n" AS "t1") '
+            'WHEN ("t1"."id" > ?) '
+            'THEN (SELECT DISTINCT COUNT("t1"."name") FROM "n" AS "t1") '
+            'ELSE (SELECT MAX("t1"."id") FROM "n" AS "t1") END AS "magic" '
+            'FROM "n" AS "t1"'), [5, 5])
+
 
 
 class TestSelectFeatures(BaseTestCase):