Odd Cannot add foreign key constraint - mysql

Question

I have an odd one. I cannot create a table using the following:
The table Users already exists in the DB, only UserTimeZones is to be added, and it fails.
CREATE TABLE `Users` (
`AccessFailedCount` int(11) NOT NULL,
`EmailConfirmed` bit(1) NOT NULL,
`Id` char(36) NOT NULL,
`NormalizedUserName` varchar(256) DEFAULT NULL,
`NormalizedEmail` varchar(256) DEFAULT NULL,
PRIMARY KEY (`Id`),
UNIQUE KEY `UserNameIndex` (`NormalizedUserName`),
KEY `EmailIndex` (`NormalizedEmail`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `UserTimeZones` (
`Id` char(36) NOT NULL,
`UserId` char(36) NOT NULL,
`TimeZoneOffsetInSeconds` int NOT NULL,
`LastUpdatedAt` datetime(6) NOT NULL,
CONSTRAINT `PK_UserTimeZones` PRIMARY KEY (`Id`),
CONSTRAINT `FK_UserTimeZones_Users_UserId` FOREIGN KEY (`UserId`) REFERENCES `Users` (`Id`) ON DELETE CASCADE
);
SHOW ENGINE INNODB STATUS;
Here is what the status shows:
------------------------ LATEST FOREIGN KEY ERROR
2018-11-09 11:26:44 0x7f832c523700 Error in foreign key constraint of
table fifty/UserTimeZones:
FOREIGN KEY (UserId) REFERENCES Users (Id) ON DELETE CASCADE ):
Cannot find an index in the referenced table where the referenced
columns appear as the first columns, or column types in the table and
the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in tables
created with >= InnoDB-4.1.12, and such columns in old tables cannot
be referenced by such columns in new tables.
Please refer to
http://dev.mysql.com/doc/refman/5.7/en/innodb-foreign-key-constraints.html
for correct foreign key definition.
So I have the classic "Cannot add foreign key constraint".
What I have tried:
Placing the Users.Id column as first column : doesn't change anything
The column types are the same, the engines too...
Applying the migration without data in the DB -> it works
Running the script in a DB without data -> still doesn't work...
What is the problem?
Not sure it matters but I use entity framework core.

Answer 1

https://dev.mysql.com/doc/refman/8.0/en/innodb-foreign-key-constraints.html
Foreign key definitions for InnoDB tables are subject to the following
conditions:
InnoDB permits a foreign key to reference any index column or group of
columns. However, in the referenced table, there must be an index
where the referenced columns are listed as the first columns in the
same order.
But oddly the index seems to be needed on the referencing table:
https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html#foreign-keys-examples
So try adding an index on your table
CREATE TABLE `UserTimeZones` (
`Id` char(36) NOT NULL,
`UserId` char(36) NOT NULL,
`TimeZoneOffsetInSeconds` int NOT NULL,
`LastUpdatedAt` datetime(6) NOT NULL,
CONSTRAINT `PK_UserTimeZones` PRIMARY KEY (`Id`),
INDEX userid_ind (UserId),
CONSTRAINT `FK_UserTimeZones_Users_UserId` FOREIGN KEY (`UserId`) REFERENCES `Users` (`Id`) ON DELETE CASCADE
);
Note: this is what the error message says.