Fix: correctly handle agg subexpressions with no selections (#2390)

sqlglot/optimizer/pushdown_projections.py

@@ -9,7 +9,9 @@
 SELECT_ALL = object()
 
 # Selection to use if selection list is empty
-DEFAULT_SELECTION = lambda: alias("1", "_")
+DEFAULT_SELECTION = lambda is_agg: alias(
+    exp.Max(this=exp.Literal.number(1)) if is_agg else "1", "_"
+)
 
 
 def pushdown_projections(expression, schema=None, remove_unused_selections=True):
@@ -98,6 +100,7 @@ def _remove_unused_selections(scope, parent_selections, schema, alias_count):
     new_selections = []
     removed = False
     star = False
+    is_agg = False
 
     select_all = SELECT_ALL in parent_selections
 
@@ -112,6 +115,9 @@ def _remove_unused_selections(scope, parent_selections, schema, alias_count):
                 star = True
             removed = True
 
+        if not is_agg and selection.find(exp.AggFunc):
+            is_agg = True
+
     if star:
         resolver = Resolver(scope, schema)
         names = {s.alias_or_name for s in new_selections}
@@ -124,7 +130,7 @@ def _remove_unused_selections(scope, parent_selections, schema, alias_count):
 
     # If there are no remaining selections, just select a single constant
     if not new_selections:
-        new_selections.append(DEFAULT_SELECTION())
+        new_selections.append(DEFAULT_SELECTION(is_agg))
 
     scope.expression.select(*new_selections, append=False, copy=False)
 

tests/fixtures/optimizer/pushdown_projections.sql

@@ -70,6 +70,15 @@ WITH cte AS (SELECT 1 AS x, 3 AS z) SELECT cte.a AS a, cte.z AS z FROM cte AS ct
 WITH cte(x, y, z) AS (SELECT 1, 2, 3) SELECT a, z FROM (SELECT * FROM cte AS cte(b)) AS cte(a);
 WITH cte AS (SELECT 1 AS x, 3 AS z) SELECT cte.a AS a, cte.z AS z FROM (SELECT cte.b AS a, cte.z AS z FROM cte AS cte(b)) AS cte;
 
+WITH y AS (SELECT a FROM x) SELECT 1 FROM y;
+WITH y AS (SELECT 1 AS _ FROM x AS x) SELECT 1 AS "1" FROM y;
+
+WITH y AS (SELECT SUM(a) FROM x) SELECT 1 FROM y;
+WITH y AS (SELECT MAX(1) AS _ FROM x AS x) SELECT 1 AS "1" FROM y;
+
+WITH y AS (SELECT a FROM x GROUP BY a) SELECT 1 FROM y;
+WITH y AS (SELECT 1 AS _ FROM x AS x GROUP BY x.a) SELECT 1 AS "1" FROM y;
+
 --------------------------------------
 -- Unknown Star Expansion
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