UCP: Support the operation of adding multi-columns

[zimulala]

Description

Support adding multi-columns in one statement, the syntax as follows:

ALTER TABLE tbl_name
    [alter_specification [, alter_specification] ...]

alter_specification:
ADD [COLUMN] (col_name column_definition,...)

We can add a new action as AddColumns to handle this DDL job. We can achieve this by referring to AddColumn action.

#3627 implementation was basically okay for the current version, if you need it, you can also use it as a reference.

Score

• 2996

Mentor(s)

• @zimulala

Contact the mentors: #tidb-challenge-program channel in TiDB Community Slack Workspace

Recommended Skills

• SQL executor
• TiDB DDL
• Golang

Learning Materials

MySQL's document for syntax reference.
TiDB DDL architecture

[shenli]

@breeswish PTAL

[breezewish]

related: #3627

[morgo]

@zimulala can we close this issue now? I assume it is in reference to composite indexes (which are supported), and not chaining multiple ddl changes at once (roadmap).

[zimulala]

@morgo I can't close this issue yet. We support composite indexes. But this issue says that it supports adding multiple columns in a statement, for example:

alter table tbl add column (c4 int default 1, c5 int);

[zimulala]

Related to issues：

• Support multiple table rename (swap table use case) #9384 Support multiple table rename (swap table use case)
• dropping column with index covered isn't fully compatible with mysql #3364 Dropping column with index covered isn't fully compatible with mysql

[gauss1314]

/pick-up-challenge

[sre-bot]

@gauss1314 pick up issue success

[gauss1314]

Hi, @zimulala , I think there are 3 kinds of add multi-columns:

1. alter table t add column (b int, c int);
2. alter table t add column b int after a, add column c int after b;
3. alter table t add column (b int, c int), add column d int after b;

This issue only mentioned first one, and I think the lack of the latter two affects usability.
But implementing all three maybe a bit difficult. So what's your suggestion？

[zimulala]

These are just the different positions of the columns. We can adjust their position uniformly at the end of processing. The special function is adjustColumnInfoInAddColumn.
This issue itself may be more complicated. If you think it is necessary, we can implement the first type of statement first.