Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

MySQL [(none)]> SET sql_auto_is_null = 1;
ERROR 1235 (42000): function sql_auto_is_null has only noop implementation in tidb now, use tidb_enable_noop_functions to enable these functions
MySQL [(none)]> set global sql_auto_is_null = 1;
Query OK, 0 rows affected (0.01 sec)

MySQL [(none)]> select @@tidb_enable_noop_functions;
+------------------------------+
| @@tidb_enable_noop_functions |
+------------------------------+
| OFF |
+------------------------------+
1 row in set (0.00 sec)

2. What did you expect to see? (Required)

session and global level setting will all be forbidden

3. What did you see instead (Required)

global level is allowed

4. What is your TiDB version? (Required)

v5.3.0