collation and flag of some functions are wrong

[xiongjiwei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a char(10) collate utf8mb4_general_ci, b char(10) collate utf8mb4_unicode_ci);
insert into t values ('a', 'a')
select concat(a, 0x80) from t;

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

mysql> select concat(a, 0x80) from t;
Field   1:  `concat(a, 0x80)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       VAR_STRING
Collation:  utf8mb4_0900_ai_ci (255)
Length:     44
Max_length: 4
Decimals:   31
Flags:


+-----------------+
| concat(a, 0x80) |
+-----------------+
| a�               |
| 一�              |
+-----------------+
2 rows in set (0.00 sec)

3. What did you see instead (Required)

Database changed
mysql> select concat(a, 0x80) from t;
Field   1:  `concat(a, 0x80)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       VAR_STRING
Collation:  binary (63)
Length:     13
Max_length: 4
Decimals:   31
Flags:      NOT_NULL BINARY


+----------------------------------+
| concat(a, 0x80)                  |
+----------------------------------+
| 0x6180                           |
| 0xE4B88080                       |
+----------------------------------+
2 rows in set (0.02 sec)

it should not be binary

4. What is your TiDB version? (Required)

[sykp241095]

Hi, will it be fixed in 5.0 GA ?

[ti-srebot]

Please edit this comment or add a new comment to complete the following information

Not a bug

1. Remove the 'type/bug' label
2. Add notes to indicate why it is not a bug

Duplicate bug

1. Add the 'type/duplicate' label
2. Add the link to the original bug

Bug

Note: Make Sure that 'component', and 'severity' labels are added
Example for how to fill out the template: #20100

1. Root Cause Analysis (RCA) (optional)

2. Symptom (optional)

3. All Trigger Conditions (optional)

4. Workaround (optional)

5. Affected versions

6. Fixed versions