different behavior on foreign key with MySQL

[csuzhangxc]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

in MySQL 5.7.21

> create database db;
Query OK, 1 row affected

> create table db.t1 (c1 int primary key, c2 int);
Query OK, 0 rows affected

> create table db.t2 (c1 int primary key, c2 int);
Query OK, 0 rows affected

> alter table db.t1 add constraint fk foreign key (c2) references t2(c1);
Query OK, 0 rows affected

> show create table db.t1\G
***************************[ 1. row ]***************************
Table        | t1
Create Table | CREATE TABLE `t1` (
  `c1` int(11) NOT NULL,
  `c2` int(11) DEFAULT NULL,
  PRIMARY KEY (`c1`),
  KEY `fk` (`c2`),
  CONSTRAINT `fk` FOREIGN KEY (`c2`) REFERENCES `t2` (`c1`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

in TiDB v4.0.0 (also for master branch with git commit 9995ad7)

> create database db;
Query OK, 1 row affected

> create table db.t1 (c1 int primary key, c2 int);
Query OK, 0 rows affected

> create table db.t2 (c1 int primary key, c2 int);
Query OK, 0 rows affected

> alter table db.t1 add constraint fk foreign key (c2) references t2(c1);
(1046, 'No database selected')

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

no error reported.

3. What did you see instead (Required)

(1046, 'No database selected')

4. Affected version (Required)

v4.0.0 (other versions are not tested)

5. Root Cause Analysis