Delete the foreign key in SQL Server

Once you have created the FOREIGN KEY but no longer use the foreign key and want to delete it, you can use the ALTER TABLE command in SQL Server (Transact-SQL).

Syntax to delete foreign keys in SQL Server

 ALTER TABLE ten_ba ng 
 DROP CONSTRAINT f k_ten; 

Variable name or variable value

ten_bang

The name of the table to which the foreign key has been created.

fk_ten

The name of the foreign key you want to delete.

For example

 CREATE TABLE sanpham 
 ( id_sanpham INT PRIMARY KEY, 
  ten_sanpham VARCHAR(50) NOT NULL, 
  phan_loai VARCHAR(25) 
 ); 
 
 CREATE TABLE hangtonkho 
 ( id_hangtonkho INT PRIMARY KEY, 
  id_sanpham INT NOT NULL, 
  soluong INT, 
  luong_toithieu INT, 
  luong_toida INT, 
  CONSTRAINT fk_htk_id_sanpham 
  FOREIGN KEY (id_sanpham) 
  REFERENCES sanpham (id_sanpham) 
 ); 

In this example, we created the parent table, sanpham, with the primary key including the information field id_sanpham. Then there is a child table named hangtonkho with a foreign key with deletion constraint. The CREATE TABLE statement creates a foreign key on the hangtonkho table named fk_htk_id_sanpham. The foreign key forms the relationship between the id_sanpham column in the hangtonkho table and id_sanpham in the sanpham table.

1. Activate foreign keys in SQL Server
2. Foreign Key (Set Null) foreign key in SQL Server
3. Foreign Key (Cascade Delete) in SQL Server

If you want to delete the foreign key fk_htk_id_sanpham, execute the command below.

 ALTER TABLE hangtonk ho 
 DROP CONSTRAINT fk_ htk_id_sanpham; 

The above ALTER TABLE statement will delete the constraint named fk_htk_id_sanpham in the hangtonkho table.

Last lesson: Foreign Key (Set Null) foreign key in SQL Server

The following article: Disable foreign key in SQL Server