ddl: fix alter table charset bug and compatibility

[crazycs520]

What problem does this PR solve?

1. Change table charset should change all column charset too.

In MySQL

mysql > create table t1 (a varchar(10) character set ascii);
Query OK, 0 rows affected
Time: 0.021s
mysql > show  create table t1
+-------+----------------------------------------------------+
| Table | Create Table                                       |
+-------+----------------------------------------------------+
| t1    | CREATE TABLE `t1` (                                |
|       |   `a` varchar(10) CHARACTER SET ascii DEFAULT NULL |
|       | ) ENGINE=InnoDB DEFAULT CHARSET=latin1             |
+-------+----------------------------------------------------+
1 row in set
Time: 0.007s
mysql > alter table t1 convert to charset utf8mb4;
Query OK, 0 rows affected
Time: 0.028s
mysql > show  create table t1
+-------+-----------------------------------------+
| Table | Create Table                            |
+-------+-----------------------------------------+
| t1    | CREATE TABLE `t1` (                     |
|       |   `a` varchar(10) DEFAULT NULL          |
|       | ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |
+-------+-----------------------------------------+
1 row in set

In TiDB

tidb > create table t1 (a varchar(10) character set ascii) charset=utf8
Query OK, 0 rows affected
Time: 0.007s
tidb > show create table t1
+-------+----------------------------------------------------------------------+
| Table | Create Table                                                         |
+-------+----------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (                                                  |
|       |   `a` varchar(10) CHARACTER SET ascii COLLATE ascii_bin DEFAULT NULL |
|       | ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin                |
+-------+----------------------------------------------------------------------+
1 row in set
Time: 0.006s
tidb > alter table t1 convert to charset utf8mb4;
Query OK, 0 rows affected
Time: 0.007s
tidb > show create table t1
+-------+----------------------------------------------------------------------+
| Table | Create Table                                                         |
+-------+----------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (                                                  |
|       |   `a` varchar(10) CHARACTER SET ascii COLLATE ascii_bin DEFAULT NULL |
|       | ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin          |
+-------+----------------------------------------------------------------------+
1 row in set
Time: 0.006s

2. The table charset maybe "" cause create in the old TiDB version(such as 2.0.8), then execute alter table charset will return error, But it should execute successfully.

3. Some behaver is not compatible with MySQL.

In MySQL

create table t (a varchar(10) character set utf8) charset=utf8;
mysql > alter table t charset latin1 charset utf8 charset utf8mb4 collate utf8_bin;
(1302, u"Conflicting declarations: 'CHARACTER SET latin1' and 'CHARACTER SET utf8'")
mysql > alter table t charset utf8mb4 collate "" collate utf8mb4_bin;
(1273, u"Unknown collation: ''")
mysql > alter table t charset utf8mb4 collate "";
(1273, u"Unknown collation: ''")
mysql > alter table t collate "";
(1273, u"Unknown collation: ''")

In TiDB v2.0.8

create table t1 (a varchar(10));

$ curl "http://$IP:10080/schema/test/t1"
{
    ...
    "charset": "",    #table charset.
    "collate": "",
    "cols": [
        {
            ...
            "id": 1,
            "name": {
                "L": "a",
                "O": "a"
            },
            ...
            "type": {
                "Charset": "utf8",  #column charset.
                "Collate": "utf8_bin",
                 ...

In TiDB master,

tidb > alter table t1 convert to charset utf8mb4;
(1105, u'unsupported modify charset from  to utf8mb4')

What is changed and how it works?

Change AlterTableCharsetAndCollate func.

Check List

Tests

• Integration test

Code changes

• Has exported function/method change

Side effects

Related changes

• Need to cherry-pick to the release branch 2.1

[codecov]

Codecov Report

Merging #9790 into master will decrease coverage by 0.0124%.
The diff coverage is 86.7469%.

@@               Coverage Diff                @@
##             master      #9790        +/-   ##
================================================
- Coverage   78.0083%   77.9959%   -0.0125%     
================================================
  Files           404        404                
  Lines         81954      82012        +58     
================================================
+ Hits          63931      63966        +35     
- Misses        13329      13341        +12     
- Partials       4694       4705        +11

[crazycs520]

/run-all-tests

[crazycs520]

/run-unit-test

[crazycs520]

/run-all-tests

[xiekeyi98]

LGTM

[winkyao]

LGTM

[bb7133]

LGTM

[zimulala]

It seems that we need to check all collates.

mysql> alter table t charset utf8 collate utf8_bin collate utf8_bin collate utf8mb4_bin;
ERROR 1253 (42000): COLLATION 'utf8mb4_bin' is not valid for CHARACTER SET 'utf8'
mysql> alter table t charset utf8 collate utf8_bin collate utf8mb4_bin collate utf8_bin;
ERROR 1253 (42000): COLLATION 'utf8mb4_bin' is not valid for CHARACTER SET 'utf8'

[zimulala]

LGTM

[zimulala]

/run-all-tests