Fix: qualifying correlated subqueries

sqlglot/optimizer/qualify_columns.py

@@ -240,7 +240,9 @@ def _qualify_columns(scope, resolver):
             # column_table can be a '' because bigquery unnest has no table alias
             if column_table:
                 column.set("table", column_table)
-        elif column_table not in scope.sources:
+        elif column_table not in scope.sources and (
+            not scope.parent or column_table not in scope.parent.sources
+        ):
             # structs are used like tables (e.g. "struct"."field"), so they need to be qualified
             # separately and represented as dot(dot(...(<table>.<column>, field1), field2, ...))
 

tests/fixtures/optimizer/qualify_columns.sql

@@ -212,6 +212,10 @@ SELECT x.a AS a FROM x AS x WHERE x.b IN (SELECT x.b AS b FROM y AS x);
 SELECT a FROM x AS i WHERE b IN (SELECT b FROM y AS j WHERE j.b IN (SELECT c FROM y AS k WHERE k.b = j.b));
 SELECT i.a AS a FROM x AS i WHERE i.b IN (SELECT j.b AS b FROM y AS j WHERE j.b IN (SELECT k.c AS c FROM y AS k WHERE k.b = j.b));
 
+# execute: false
+SELECT (SELECT n.a FROM n WHERE n.id = m.id) FROM m AS m;
+SELECT (SELECT n.a AS a FROM n AS n WHERE n.id = m.id) AS _col_0 FROM m AS m;
+
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