blob/text/int length isn't accuracy in column metadata

[lysu]

1. What did you do?

connection tidb with --column-type-info

create table bitest(b blob(2));
select * from bitest;

2. What did you expect to see?

Length:     255

3. What did you see instead?

Length:     8

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

2.0.6

ref #7463

[ghost]

Confirming this issue is still present in master:

mysql> create table bitest(b blob(2));
Query OK, 0 rows affected (0.11 sec)

mysql> select * from bitest;
Field   1:  `b`
Catalog:    `def`
Database:   `test`
Table:      `bitest`
Org_table:  `bitest`
Type:       BLOB
Collation:  binary (63)
Length:     2
Max_length: 0
Decimals:   0
Flags:      NOT_NULL BINARY 


0 rows in set (0.00 sec)

mysql> SHOW CREATE TABLE bitest\G
*************************** 1. row ***************************
       Table: bitest
Create Table: CREATE TABLE `bitest` (
  `b` blob DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
1 row in set (0.00 sec)

mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-835-g1fed1fb89
Edition: Community
Git Commit Hash: 1fed1fb895e133f5a5e6818ac24087b7c3a0d4f8
Git Branch: master
UTC Build Time: 2020-07-24 03:27:11
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

[dveeden]

Looks like this might have been fixed:

mysql> create table bitest(b blob(2));
Query OK, 0 rows affected (0.01 sec)

mysql> select * from bitest;
Field   1:  `b`
Catalog:    `def`
Database:   `test`
Table:      `bitest`
Org_table:  `bitest`
Type:       TINY_BLOB
Collation:  binary (63)
Length:     255
Max_length: 0
Decimals:   0
Flags:      BINARY 


0 rows in set (0.00 sec)

mysql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v5.3.0-alpha-1209-g19a2b3c31
Edition: Community
Git Commit Hash: 19a2b3c31106470f83696f8fdaf443f150061a66
Git Branch: master
UTC Build Time: 2021-10-26 12:13:58
GoVersion: go1.16.8
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)