Type consistency with MySQL: by creating view and describing it

Bug Report

I would like to know if there is any documentation describing the type compatibility with mysql.

1. Minimal reproduce step (Required)

create view v1 as select 1;
desc v1;
create view v2 as select 'a';
desc v2;
create view v3 as select 'a' union select 'bc';
desc v3;
create view v4 as select 'a' union select 1;
desc v4;

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

In MySQL:

+-------+------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------+------+-----+---------+-------+
| 1     | int  | NO   |     | 0       |       |
+-------+------+------+-----+---------+-------+
1 row in set (0.01 sec)

+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a     | varchar(1) | NO   |     |         |       |
+-------+------------+------+-----+---------+-------+
1 row in set (0.03 sec)

+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a     | varchar(2) | NO   |     |         |       |
+-------+------------+------+-----+---------+-------+
1 row in set (0.03 sec)

+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a     | varchar(1) | NO   |     |         |       |
+-------+------------+------+-----+---------+-------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

In TiDB:

+-------+-----------+------+------+---------+-------+
| Field | Type      | Null | Key  | Default | Extra |
+-------+-----------+------+------+---------+-------+
| 1     | bigint(1) | NO   |      | NULL    |       |
+-------+-----------+------+------+---------+-------+
1 row in set (0.03 sec)

+-------+------------+------+------+---------+-------+
| Field | Type       | Null | Key  | Default | Extra |
+-------+------------+------+------+---------+-------+
| a     | varchar(1) | NO   |      | NULL    |       |
+-------+------------+------+------+---------+-------+
1 row in set (0.03 sec)

+-------+------------+------+------+---------+-------+
| Field | Type       | Null | Key  | Default | Extra |
+-------+------------+------+------+---------+-------+
| a     | varchar(2) | YES  |      | NULL    |       |
+-------+------------+------+------+---------+-------+
1 row in set (0.01 sec)

+-------+-------------+------+------+---------+-------+
| Field | Type        | Null | Key  | Default | Extra |
+-------+-------------+------+------+---------+-------+
| a     | varchar(20) | YES  |      | NULL    |       |
+-------+-------------+------+------+---------+-------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()
                                                                                                                                                 |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v5.2.0-alpha-88-ged52601e6
Edition: Community
Git Commit Hash: ed52601e6eb560138db8cdccdfa1b5e2d33a11f0
Git Branch: master
UTC Build Time: 2021-06-16 13:03:48
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.03 sec)