restrictions on partitioning in CREATE TABLE can be bypass with ALTER TABLE

[time-and-fate]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a varchar(20), b int) partition by hash(a) partitions 2; -- fail
create table t(a varchar(20), b int);
alter table t partition by hash(a) partitions 2; -- success

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

Both succeed or both fail.

3. What did you see instead (Required)

> create table t(a varchar(20), b int) partition by hash(a) partitions 2;
ERROR 1659 (HY000): Field 'a' is of a not allowed type for this type of partitioning
> create table t(a varchar(20), b int);
Query OK, 0 rows affected (0.045 sec)

> alter table t partition by hash(a) partitions 2;
Query OK, 0 rows affected, 1 warning (1.080 sec)

> show create table t;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                   |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t     | CREATE TABLE `t` (
  `a` varchar(20) DEFAULT NULL,
  `b` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
PARTITION BY HASH (`a`) PARTITIONS 2 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.001 sec)

4. What is your TiDB version? (Required)

nightly