types: port 'HasCharset' function from MySQL

[bb7133]

What problem does this PR solve?

This PR aims to solve the some known show charset/collation issues in TiDB, for example, pingcap/tidb#9837

What is changed and how it works?

A HasCharset function is ported from MySQL source, for example:

Field::has_charset()

Field_string::has_charset()

This function can be used in the procedure of some show-schema executions, for example, in MySQL it decides where a given column's Collation result is NULL in show full columns statement:

sql_show.cc::store_column_type()

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported function/method change

Side effects

• None

Related changes

• Need to cherry-pick to the release branch

[xiekeyi98]

This line is too long, maybe we could spilit it into two.

[bb7133]

How about this?

    case                                                                               
        mysql.TypeVarchar,    
        mysql.TypeString,    
        mysql.TypeVarString,    
        mysql.TypeBlob,    
        mysql.TypeTinyBlob,     
        mysql.TypeMediumBlob,     
        mysql.TypeLongBlob:    
        return !mysql.HasBinaryFlag(ft.Flag)    
    case                     
        mysql.TypeEnum,    
        mysql.TypeSet:    
        return true 

[xiekeyi98]

I think to keep consistent with Golang is enough.
For example:
https://github.com/golang/go/blob/50bd1c4d4eb4fac8ddeb5f063c099daccfb71b26/src/go/types/return.go#L17-L28

[crazycs520]

After this PR, I think there is something need attention. @xiekeyi98

create table t (
a bit(11),
b int,
c int(3),
d float,
e double,
f decimal(10,2),
g numeric(10,2),
h date,
i datetime,
j timestamp,
k time,
m year,
c0 char(10),
c1 varchar(10),
c2 binary(10),
c3 varbinary(10),
c4 blob(50),
c5 text(50),
c6 ENUM('value1','value2'),
c7 SET('value1','value2'),
c8 JSON
) charset="utf8mb4"

In MySQL:

test> show full columns from t;
+-------+-------------------------+--------------------+------+-----+-------------------+-----------------------------+---------------------------------+---------+
| Field | Type                    | Collation          | Null | Key | Default           | Extra                       | Privileges                      | Comment |
+-------+-------------------------+--------------------+------+-----+-------------------+-----------------------------+---------------------------------+---------+
| a     | bit(11)                 | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| b     | int(11)                 | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| c     | int(3)                  | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| d     | float                   | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| e     | double                  | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| f     | decimal(10,2)           | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| g     | decimal(10,2)           | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| h     | date                    | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| i     | datetime                | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| j     | timestamp               | <null>             | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP | select,insert,update,references |         |
| k     | time                    | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| m     | year(4)                 | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| c0    | char(10)                | utf8mb4_general_ci | YES  |     | <null>            |                             | select,insert,update,references |         |
| c1    | varchar(10)             | utf8mb4_general_ci | YES  |     | <null>            |                             | select,insert,update,references |         |
| c2    | binary(10)              | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| c3    | varbinary(10)           | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| c4    | tinyblob                | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
| c5    | tinytext                | utf8mb4_general_ci | YES  |     | <null>            |                             | select,insert,update,references |         |
| c6    | enum('value1','value2') | utf8mb4_general_ci | YES  |     | <null>            |                             | select,insert,update,references |         |
| c7    | set('value1','value2')  | utf8mb4_general_ci | YES  |     | <null>            |                             | select,insert,update,references |         |
| c8    | json                    | <null>             | YES  |     | <null>            |                             | select,insert,update,references |         |
+-------+-------------------------+--------------------+------+-----+-------------------+-----------------------------+---------------------------------+---------+

In TiDB

+-------+-------------------------+-------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type                    | Collation   | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+-------------------------+-------------+------+-----+---------+-------+---------------------------------+---------+
| a     | bit(11)                 | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| b     | int(11)                 | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| c     | int(3)                  | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| d     | float                   | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| e     | double                  | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| f     | decimal(10,2)           | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| g     | decimal(10,2)           | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| h     | date                    | NULL        | YES  |     | <null>  |       | select,insert,update,references |         |
| i     | datetime                | NULL        | YES  |     | <null>  |       | select,insert,update,references |         |
| j     | timestamp               | NULL        | YES  |     | <null>  |       | select,insert,update,references |         |
| k     | time                    | NULL        | YES  |     | <null>  |       | select,insert,update,references |         |
| m     | year(4)                 | NULL        | YES  |     | <null>  |       | select,insert,update,references |         |
| c0    | char(10)                | utf8mb4_bin | YES  |     | <null>  |       | select,insert,update,references |         |
| c1    | varchar(10)             | utf8mb4_bin | YES  |     | <null>  |       | select,insert,update,references |         |
| c2    | binary(10)              | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| c3    | varbinary(10)           | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| c4    | blob                    | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
| c5    | text                    | utf8mb4_bin | YES  |     | <null>  |       | select,insert,update,references |         |
| c6    | enum('value1','value2') | utf8mb4_bin | YES  |     | <null>  |       | select,insert,update,references |         |
| c7    | set('value1','value2')  | utf8mb4_bin | YES  |     | <null>  |       | select,insert,update,references |         |
| c8    | json                    | binary      | YES  |     | <null>  |       | select,insert,update,references |         |
+-------+-------------------------+-------------+------+-----+---------+-------+---------------------------------+---------+

[xiekeyi98]

Yep.
Maybe something should be refactored.
Thanks for your guidance.
❤️

[bb7133]

addressed, thank you @xiekeyi98

[xiekeyi98]

LGTM.

[winkyao]

LGTM，well done.