Creating functional index with null column name worked in tidb

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE t(a INT, b INT, INDEX c((null)));

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

mysql> CREATE TABLE t(a INT, b INT, INDEX c((null)));
ERROR 3761 (HY000): The used storage engine cannot index the expression 'NULL'.

3. What did you see instead (Required)

mysql> CREATE TABLE t(a INT, b INT, INDEX c((null)));
Query OK, 0 rows affected (0.07 sec)

mysql> show create table t;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                              |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| t     | CREATE TABLE `t` (
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL,
  KEY `c` ((null))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

| Release Version: v5.3.0
Edition: Community
Git Commit Hash: 4a1b2e9fe5b5afb1068c56de47adb07098d768d6
Git Branch: heads/refs/tags/v5.3.0
UTC Build Time: 2021-11-24 13:31:24
GoVersion: go1.16.5
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |