无法删除或更新父行：外键约束失败

Question

每次尝试创建调查表时，我都会不断收到此错误无法删除或更新父行：外键约束失败。

表-用户

users (
username VARCHAR(16), 
password VARCHAR(16), 
email VARCHAR(64),
first_name VARCHAR(32),
surname VARCHAR(64),
telephone VARCHAR(16),
dob DATE,user_type 
VARCHAR(6),
PRIMARY KEY(username)),

表格-调查

CREATE TABLE survey 
(id  INT NOT NULL AUTO_INCREMENT, 
title VARCHAR(64), 
type VARCHAR(40),
PRIMARY KEY(id)
FOREIGN KEY(username)
REFERENCES users(username)),