sql drop foreign key constraint code example

Example 1: drop foreign key

ALTER TABLE table_name
DROP CONSTRAINT fk_name;

Example 2: how to remove foreign key constraint in sql

USE AdventureWorks2012;  
GO  
ALTER TABLE dbo.DocExe   
DROP CONSTRAINT FK_Column_B;   
GO

Example 3: foreign key in sql

A FOREIGN KEY is a key used to link two tables together.
A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
The table containing the foreign key is called the child table, and the table containing the candidate key is called the referenced or parent table.

Example:
# creating table users
CREATE TABLE users(
	user_id INT NOT NULL,
  	user_name VARCHAR(64) NOT NULL,
  	user_pass VARCHAR(32) NOT NULL,
  	PRIMARY KEY(user_id);
);
# adding user data
INSERT INTO users VALUES(1,"Raj","raj@123");

# creating table orders
CREATE TABLE orders(
	order_id INT NOT NULL,
  	order_description VARCHAR(255),
  	orderer_id INT NOT NULL,
  	PRIMARY KEY(order_id),
  	FOREIGN KEY (orderer_id) REFERENCES users(user_id)
);
# adding order data
INSERT INTO orders VALUES(1,"Daily groceries",1);

Example 4: alter table add column forigen key mysql

ALTER TABLE tryholpz_demo07.core_modules 
ADD COLUMN belongs_to_role INT, 
ADD FOREIGN KEY core_modules(belongs_to_role) REFERENCES role_specific_modules_info(id) ON DELETE CASCADE