feat(clickhouse): transform function support (#4408)

* feat!: make transform function accept variable amount of expressions

* feat(clickhouse): transform function support

* Pop transform instead of adding an entry

---------

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

Author: GaliFFun

sqlglot/dialects/clickhouse.py

@@ -275,6 +275,7 @@ class Parser(parser.Parser):
             "EDITDISTANCE": exp.Levenshtein.from_arg_list,
             "LEVENSHTEINDISTANCE": exp.Levenshtein.from_arg_list,
         }
+        FUNCTIONS.pop("TRANSFORM")
 
         AGG_FUNCTIONS = {
             "count",

tests/dialects/test_clickhouse.py

@@ -1253,3 +1253,9 @@ def test_window_functions(self):
         self.validate_identity(
             "SELECT row_number() OVER (PARTITION BY column2 ORDER BY column3) FROM table"
         )
+
+    def test_functions(self):
+        self.validate_identity("SELECT TRANSFORM(foo, [1, 2], ['first', 'second']) FROM table")
+        self.validate_identity(
+            "SELECT TRANSFORM(foo, [1, 2], ['first', 'second'], 'default') FROM table"
+        )