fix: remove EXPRESSION column dependency in get_indexes_sql()

The EXPRESSION column in information_schema.STATISTICS only exists in
MySQL 8.0.13+. Using it breaks @Schema decoration on MySQL < 8.0.13 and
MariaDB. Use COLUMN_NAME directly; functional indexes with NULL column
names are already filtered out downstream.

Fixes #1436

Author: dimitri-yatsenko

src/datajoint/adapters/mysql.py

@@ -737,12 +737,14 @@ def parse_foreign_key_error(self, error_message: str) -> dict[str, str | list[st
     def get_indexes_sql(self, schema_name: str, table_name: str) -> str:
         """Query to get index definitions.
 
-        Note: For MySQL 8.0+, EXPRESSION column contains the expression for
-        functional indexes. COLUMN_NAME is NULL for such indexes.
+        Uses COLUMN_NAME only for compatibility with MySQL < 8.0.13 and MariaDB,
+        which lack the EXPRESSION column in information_schema.STATISTICS.
+        Functional indexes (MySQL 8.0.13+) will have COLUMN_NAME = NULL and are
+        filtered out downstream.
         """
         return (
             f"SELECT INDEX_NAME as index_name, "
-            f"COALESCE(COLUMN_NAME, CONCAT('(', EXPRESSION, ')')) as column_name, "
+            f"COLUMN_NAME as column_name, "
             f"NON_UNIQUE as non_unique, SEQ_IN_INDEX as seq_in_index "
             f"FROM information_schema.statistics "
             f"WHERE table_schema = {self.quote_string(schema_name)} "