Create & Drop a Foreign Key - SQL Query

I) How to create a Foreign Key in SQL?

Using Create table statement.

Step 1: Create a table Supplier.

CREATE TABLE Supplier
( S_Id INT not null,
  S_Name varchar2(50) not null,
  contact_Person varchar2(50),
  CONSTRAINT supplier_pk PRIMARY KEY (S_ID)
);


In the above query the table Supplier is created and primary key is created on column Supplier_id.

Step 2: Create a table Products and create a foreign key on column supplier_id.

CREATE TABLE Products
( Product_id INT not null,
  S_Id numeric(10) not null,
  CONSTRAINT fk_supplier
    FOREIGN KEY (S_Id)
    REFERENCES Supplier(S_ID)
);


In the above query the foreign key is created on S_ID column by taking REFERENCES Supplier(S_ID).

II) How to drop foreign key?

ALTER TABLE Products DROP CONSTRAINT fk_supplier;

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