Fix(clickhouse): improve struct type parsing (#3547)

sqlglot/parser.py

@@ -4274,7 +4274,7 @@ def _parse_types(
 
         if self._match(TokenType.L_PAREN):
             if is_struct:
-                expressions = self._parse_csv(self._parse_struct_types)
+                expressions = self._parse_csv(lambda: self._parse_struct_types(type_required=True))
             elif nested:
                 expressions = self._parse_csv(
                     lambda: self._parse_types(
@@ -4392,15 +4392,16 @@ def _parse_struct_types(self, type_required: bool = False) -> t.Optional[exp.Exp
             or self._parse_id_var()
         )
         self._match(TokenType.COLON)
-        column_def = self._parse_column_def(this)
 
-        if type_required and (
-            (isinstance(this, exp.Column) and this.this is column_def) or this is column_def
+        if (
+            type_required
+            and not isinstance(this, exp.DataType)
+            and not self._match_set(self.TYPE_TOKENS, advance=False)
         ):
             self._retreat(index)
             return self._parse_types()
 
-        return column_def
+        return self._parse_column_def(this)
 
     def _parse_at_time_zone(self, this: t.Optional[exp.Expression]) -> t.Optional[exp.Expression]:
         if not self._match_text_seq("AT", "TIME", "ZONE"):

tests/dialects/test_clickhouse.py

@@ -42,6 +42,7 @@ def test_clickhouse(self):
         self.assertEqual(expr.sql(dialect="clickhouse"), "COUNT(x)")
         self.assertIsNone(expr._meta)
 
+        self.validate_identity("SELECT CAST(x AS Tuple(String, Array(Nullable(Float64))))")
         self.validate_identity("countIf(x, y)")
         self.validate_identity("x = y")
         self.validate_identity("x <> y")