create table UserTable(
	userID varchar(30) not null,
    userPassword varchar(100) not null,
    userDeadline date not null,
    userEmail varchar(30) not null,
    
    primary key(userID)
);
create table UsernameTable(
	userID varchar(30) not null,
	userClusterName varchar(10) not null unique,
    
    primary key(userID),
    foreign key(userID) references UserTable(userID) ON DELETE CASCADE
);
create table MessageTable(
		messageID integer not null auto_increment,
    userID varchar(30) not null,
    senderNickname varchar(30) not null,
    senderClusterName varchar(10) not null,
		messageTitle varchar(30) not null,
    messageText varchar(2000) not null,
    
    primary key(messageID),
    foreign key(userID) references UserTable(userID) ON DELETE CASCADE
);

42memory (erdcloud.com)