Cannot add foreign key constraint error - mysql

Question

In the given Images, There are two tables. In the table STUD_MEMBER, Dept_ID is a foreign key which is referring to Dept_ID in table DEPARTMENT.:
So when I add foreign key constraints in mysql at phpmyadmin like
CREATE TABLE DEPARTMENT(
Dept_ID INT,
Dept_Name VARCHAR(25));
INSERT INTO DEPARTMENT VALUES(1,"Information Technology");
INSERT INTO DEPARTMENT VALUES(2,"Electrical");
INSERT INTO DEPARTMENT VALUES(3,"Civil");
INSERT INTO DEPARTMENT VALUES(4,"Mechanical");
INSERT INTO DEPARTMENT VALUES(5,"Chemical");
CREATE TABLE STUD_MEMBER(
Roll_No INT NOT NULL PRIMARY KEY,
FName VARCHAR(20),
MName VARCHAR(20),
SName VARCHAR(20),
Dept_ID INT,
FOREIGN KEY (Dept_ID) REFERENCES DEPARTMENT(Dept_ID),
Semester INT,
Contact_No INT,
Gender VARCHAR(6));
It is showing an error that 1215- cannot add foreign key constraint. As far as I know, it is the correct way to add a foreign key, I am so confused why it is wrong. Please help in solving this.

Answer 1

It looks like the referenced column has to be either a primary key, or it has to have a unique index. The following CREATE TABLE statement worked for me:
CREATE TABLE DEPARTMENT (
Dept_ID INT PRIMARY KEY NOT NULL,
Dept_Name VARCHAR(25)
);

Answer 2

if you are defining foreign key in child, the parent field must have an index defined on it.
check reference from HERE
[CONSTRAINT [symbol]] FOREIGN KEY
[index_name] (index_col_name, ...)
REFERENCES tbl_name (index_col_name,...)
[ON DELETE reference_option]
[ON UPDATE reference_option]
reference_option:
RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT