title: If Foreign Key Not Exist Then Add Foreign Key Constraint(Or Drop a Foreign Key Constraint If Exist) without using Name?
body: <p>I am finding difficulties to creating a a query. Let say I have a Products and Brands table. I can add a foreign key using this command,</p>
  
  <pre><code>          ALTER TABLE Products
            ADD FOREIGN KEY (BrandID)
            REFERENCES Brands(ID)
  </code></pre>
  
  <p>But I need to only run this command if Foreign Key does not exist. 
  A similar thing I need is that drop a Foreign Key Constraint If Exist without using name.</p>