Method 1: create table student(studid int primary key auto_increment,studname varchar(50));

Method 2: create table student(studid int,studname varchar(50));
alter table student add primary key(studid);

Method 3 : To remove Primary key constraint from table
alter table student drop primary key;

Note : If auto_increment is enabled on the column than , drop command on primary key is not working, so try to remove primary key constraint, do not enable auto_increment option.

Method : create table student(studid int primary key auto_increment,studname varchar(50),mobileno bigint);

Now to apply the UNIQUE key on the column
alter table student add UNIQUE(mobileno);

To remove UNIQUE key use this command first run in mysql and see the exact index name of columm
SHOW CREATE TABLE stud;
Or
SHOW INDEX FROM stud;
after executing this command we get Key_name column name and mysql will tell u the exact indexname for that column.
Query : ALTER TABLE stud DROP INDEX mobileno;

Create table Student(studid int primary key,studentname varchar(50));

Create table UT1(ut1id int, fk_studid int, Maths int);

alter table ut1 add foreign key(fk_studid) references Student(studid);

# Removing Primary Key and Foreign Key – Step by Step

Suppose we have two tables:

### Step 1: Create the Student table


CREATE TABLE Student (
    studid INT PRIMARY KEY,
    studentname VARCHAR(50)
);


Here, `studid` is the **Primary Key** of the `Student` table.

---

### Step 2: Create the UT1 table

CREATE TABLE UT1 (
    ut1id INT,
    fk_studid INT,
    Maths INT
);


Here, `fk_studid` is initially a normal column.

---

### Step 3: Add a Foreign Key to the UT1 table

ALTER TABLE UT1
ADD FOREIGN KEY (fk_studid)
REFERENCES Student(studid);


Now `fk_studid` in the `UT1` table becomes a **Foreign Key** that references `studid` in the `Student` table.

The relationship is:


Student
  studid (Primary Key)
       ↑
       │
       │ Foreign Key
       │
UT1
  fk_studid


---

# Removing Both Keys

If we want to remove **both the Foreign Key and the Primary Key**, we should remove them in the following order:

### Step 4: Find the Foreign Key name

Run:


SHOW CREATE TABLE UT1;


MySQL may show a Foreign Key name such as:


ut1_ibfk_1

The exact name may be different in your database.

---

### Step 5: Remove the Foreign Key from UT1

Use the Foreign Key name obtained in Step 4:


ALTER TABLE UT1
DROP FOREIGN KEY ut1_ibfk_1;


Now the Foreign Key relationship between `UT1` and `Student` has been removed.

---

### Step 6: Remove the Primary Key from Student

Now remove the Primary Key:


ALTER TABLE Student
DROP PRIMARY KEY;


The Primary Key on `studid` is now removed.

---

# Important Rule

When removing both keys, follow this order:


First → Remove Foreign Key from UT1
                 ↓
Second → Remove Primary Key from Student


**Why?**

Because the Foreign Key in `UT1` depends on the Primary Key in `Student`.

Therefore, the **dependent key (Foreign Key) should be removed first**, followed by the **referenced key (Primary Key)**.