ddl: refine error messages in unsupported column options

[tangenta]

What problem does this PR solve?

Fix #10731 and fix #11052.

What is changed and how it works?

1. Add more cases in switch in processColumnOptions(), avoiding the obscure error message in unsupported modify column %!s(ast.ColumnOptionType=12) #10731.

2. getModifiableColumnJob() is used to build a ActionModifyColumn DDL job. It contains two methods:

   • modifiable(), check whether the FieldType of the origin column can be changed into the new column. The checks include charset, collation, types, Flen/Decimal, etc.
   • processColumnOptions(), set FieldType of the new column, according to Option in ColumnDef, which is filled by SQL parser.

   Obviously, we should first set the FieldType and then check it. So processColumnOptions() should come first.

Check List

Tests

• Unit test
• Integration test

Related changes

• Need to cherry-pick to the release branch

[codecov]

Codecov Report

Merging #11065 into master will decrease coverage by 0.3395%.
The diff coverage is 66.6666%.

@@               Coverage Diff                @@
##             master     #11065        +/-   ##
================================================
- Coverage   81.5925%   81.2529%   -0.3396%     
================================================
  Files           424        423         -1     
  Lines         91626      90025      -1601     
================================================
- Hits          74760      73148      -1612     
- Misses        11540      11578        +38     
+ Partials       5326       5299        -27

[winkyao]

LGTM

[AilinKid]

I have tried following SQL on the code, but got following error:
ERROR 1105 (HY000): unsupported modify collate from utf8mb4_bin to utf8mb4_general_ci
Maybe be we should put the modifiable() func first, and that's actually works.

CREATE TABLE t6(a char(1))DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ;

ALTER TABLE t6 MODIFY COLUMN a char(1) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci ;

[tangenta]

@AilinKid Which TiDB version did you use?

mysql root@127.0.0.1:test> CREATE TABLE t6(a char(1))DEFAULT CHARSET=utf8mb4 COL
                           LATE=utf8mb4_general_ci ;                            
Query OK, 0 rows affected
Time: 0.014s
mysql root@127.0.0.1:test> ALTER TABLE t6 MODIFY COLUMN a char(1) CHARACTER SET 
                           utf8mb4 COLLATE utf8mb4_general_ci ;                 
Query OK, 0 rows affected
Time: 0.014s
mysql root@127.0.0.1:test> select tidb_version();                               
1 row in set
Time: 0.029s
mysql root@127.0.0.1:test> select tidb_version();                                                                                                                                                                                                             
+--------------------------------------------------------------------------+
| tidb_version()                                                           |
+--------------------------------------------------------------------------+
| Release Version: v3.0.0-rc.1-309-g34720acda                              |
| Git Commit Hash: 34720acda1eec86ff93494c8890cb2a1b4d6d478                |
| Git Branch: changing-collation                                           |
| UTC Build Time: 2019-07-10 09:12:23                                      |
| GoVersion: go version go1.12.5 linux/amd64                               |
| Race Enabled: false                                                      |
| TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e |
| Check Table Before Drop: false                                           |
+--------------------------------------------------------------------------+
1 row in set
Time: 0.015s

git log:

commit 34720acda1eec86ff93494c8890cb2a1b4d6d478 (HEAD -> changing-collation, origin/changing-collation)
Author: tangenta <tangenta@126.com>
Date:   Wed Jul 10 15:39:13 2019 +0800

    refine error message

[tangenta]

/run-all-tests

[crazycs520]

LGTM

[AilinKid]

LGTM

[zimulala]

LGTM

[sre-bot]

It seems that, not for sure, we failed to cherry-pick this commit to release-2.1. Please comment '/run-cherry-picker' to try to trigger the cherry-picker if we did fail to cherry-pick this commit before. @tangenta PTAL.