title: In oracle procedure, check if the row with primary key exists, if key already exists raise exception
body: <p>I have a procedure to insert a row in a table. I make various checks and if everything passes it inserts a row into the table.</p>
  
  <p>One of the checks is to check if a row with primary key already exists in the table. If row with primary key already exists the procedure should be able to catch it and raise error. </p>
  
  <p>What will be the best way to do so?</p>