pingcap/tidb

unsupported add column 'name' constraint UNIQUE KEY when altering

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#30,188 opened on Nov 26, 2021

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help wantedsig/sql-infratype/enhancement

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Description

Bug Report

It works fine on MySQL but reports an error on TiDB.

1. Minimal reproduce step (Required)

create table t2(id int);
ALTER TABLE `t2` ADD COLUMN `name` varchar(255) UNIQUE;

2. What did you expect to see? (Required)

No error.

3. What did you see instead (Required)

(8200, "unsupported add column 'name' constraint UNIQUE KEY when altering 'test.t2'")

4. What is your TiDB version? (Required)

tidb_version() | Release Version: v5.1.2
Edition: Community
Git Commit Hash: dc079337ef0c9d78eec2d2acb1eb31e12117d29b
Git Branch: heads/refs/tags/v5.1.2
UTC Build Time: 2021-09-27 02:47:40
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

Contributor guide

Research direction
Examine the ALTER TABLE parser and executor in TiDB's source code to identify why adding a column with UNIQUE constraint is unsupported. Look at the ddl package for column addition logic.
Tech stack
gosql
Domain
backenddatabase
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GoSQLTiDB internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60