title: ignoring condition in where clause in mysql
body: <p>Can we write conditional where clause in mysql?
  I know one way i.e with CASE WHEN</p>
  
  <p>But my condition is if where clause fails then ignore it and execute query as there was no where clause</p>
  
  <p>eg.
  I want to select persons in particular city. but if I got city null as input then ignore that statement and return all persons in all cities</p>
  
  <p>Can someone please tell me how to do this</p>
  
  <p>please Help!!</p>