ddl: Fix default value of a newly added enum column

[blacktear23]

What problem does this PR solve?

Issue Number: close #20741

Problem Summary:

The default value for new add enum column not perform correctly.

What is changed and how it works?

What's Changed:

Check column's type if is Enum just use first element for default value.

Related changes

• No

Check List

Tests

• Integration test

Side effects

• No

Release note

• Set correct default value for new added enum column.

[wjhuang2016]

/reward 600

[ti-challenge-bot]

Reward success.

[wjhuang2016]

I think Set also has this problem, could you fix it together?

[blacktear23]

I just compared with mysql, current logic's result is same as mysql.

below is mysql result:

mysql> create table t (id int primary key, c int);
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t (id, c) values (1, 1), (2, 2);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> alter table t add column cc set('a','b','c','d') not null;
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> update t set c = 2 where id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from t;
+----+------+----+
| id | c    | cc |
+----+------+----+
|  1 |    2 |    |
|  2 |    2 |    |
+----+------+----+
2 rows in set (0.00 sec)

mysql> select * from t where cc = 0;
+----+------+----+
| id | c    | cc |
+----+------+----+
|  1 |    2 |    |
|  2 |    2 |    |
+----+------+----+
2 rows in set (0.00 sec)

mysql> select * from t where cc = 1;
Empty set (0.00 sec)

mysql> insert into t (id, c) values (3, 3);
ERROR 1364 (HY000): Field 'cc' doesn't have a default value

Then TiDB result:

mysql> create table t (id int primary key, c int);
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t (id, c) values (1, 1), (2, 2);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> alter table t add column cc set('a','b','c','d') not null;
Query OK, 0 rows affected (0.01 sec)

mysql> update t set c = 2 where id = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from t;
+----+------+----+
| id | c    | cc |
+----+------+----+
|  1 |    2 |    |
|  2 |    2 |    |
+----+------+----+
2 rows in set (0.00 sec)

mysql> select * from t where cc = 0;
+----+------+----+
| id | c    | cc |
+----+------+----+
|  1 |    2 |    |
|  2 |    2 |    |
+----+------+----+
2 rows in set (0.00 sec)

mysql> select * from t where cc = 1;
Empty set (0.00 sec)

mysql> insert into t (id, c) values (3, 3);
ERROR 1364 (HY000): Field 'cc' doesn't have a default value

[wjhuang2016]

Please add these results as a test.

[blacktear23]

@wjhuang2016 after I add some debug log I found when create table the OriginDefaultValue is nil and then insert some records it can use enum first element as default value. But when execute alter table add column, we should set OriginDefaultValue to enum's first element explicit. That makes me feel strange.

[wjhuang2016]

@wjhuang2016 after I add some debug log I found when create table the OriginDefaultValue is nil and then insert some records it can use enum first element as default value. But when execute alter table add column, we should set OriginDefaultValue to enum's first element explicit. That makes me feel strange.

Yeah, this is an optimization. Add column can be done quickly.

[blacktear23]

@wjhuang2016 after I add some debug log I found when create table the OriginDefaultValue is nil and then insert some records it can use enum first element as default value. But when execute alter table add column, we should set OriginDefaultValue to enum's first element explicit. That makes me feel strange.

Yeah, this is an optimization. Add column can be done quickly.

Do we need add OriginDefaultValue when create table?

[wjhuang2016]

@wjhuang2016 after I add some debug log I found when create table the OriginDefaultValue is nil and then insert some records it can use enum first element as default value. But when execute alter table add column, we should set OriginDefaultValue to enum's first element explicit. That makes me feel strange.

Yeah, this is an optimization. Add column can be done quickly.

Do we need add OriginDefaultValue when create table?

No

[blacktear23]

@wjhuang2016 PTAL

[wjhuang2016]

LGTM

[bb7133]

LGTM

[bb7133]

PTAL @xhebox @tangenta

[xhebox]

LGTM

[wjhuang2016]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@blacktear23 merge failed.

[blacktear23]

/run-all-tests

[wjhuang2016]

/run-all-tests

[wjhuang2016]

/run-unit-test

[bb7133]

/merge

[ti-srebot]

/run-all-tests

[ti-challenge-bot]

@blacktear23, Congratulations, you get 600 in this PR, and your total score is 600 in challenge program.

[ti-srebot]

cherry pick to release-4.0 in PR #20998

[ti-srebot]

cherry pick to release-3.0 in PR #20999