fix(clickhouse): Allow TokenType.SELECT as a Tuple field identifier (#3766)

* fix(clickhouse): Allow TokenType.SELECT as a Tuple identifier

* Copy RESERVED_TOKENS only once

* Update sqlglot/dialects/clickhouse.py

---------

Co-authored-by: Jo <[email protected]>

Author: VaggelisD

sqlglot/dialects/clickhouse.py

@@ -332,6 +332,8 @@ class Parser(parser.Parser):
             TokenType.SET,
         }
 
+        RESERVED_TOKENS = parser.Parser.RESERVED_TOKENS - {TokenType.SELECT}
+
         AGG_FUNC_MAPPING = (
             lambda functions, suffixes: {
                 f"{f}{sfx}": (f, sfx) for sfx in (suffixes + [""]) for f in functions

tests/dialects/test_clickhouse.py

@@ -451,6 +451,10 @@ def test_clickhouse(self):
         self.validate_identity("ALTER TABLE visits REPLACE PARTITION ID '201901' FROM visits_tmp")
         self.validate_identity("ALTER TABLE visits ON CLUSTER test_cluster DROP COLUMN col1")
 
+        self.assertIsInstance(
+            parse_one("Tuple(select Int64)", into=exp.DataType, read="clickhouse"), exp.DataType
+        )
+
     def test_cte(self):
         self.validate_identity("WITH 'x' AS foo SELECT foo")
         self.validate_identity("WITH ['c'] AS field_names SELECT field_names")
@@ -548,6 +552,7 @@ def test_ddl(self):
         self.validate_identity(
             "CREATE TABLE foo (x UInt32) TTL time_column + INTERVAL '1' MONTH DELETE WHERE column = 'value'"
         )
+        self.validate_identity("CREATE TABLE named_tuples (a Tuple(select String, i Int64))")
 
         self.validate_all(
             """