title: Rails - execute multiple queries in a single connection
body: <p>How do I issue multiple SQL queries in a single database connection in Rails? My problem is, I  have multiple records(about 200 or more records) to be checked with the database table's existing records(I am checking composite primary key values) I could use ActiveRecord's exists? method in a single transaction block. But I don't know whether ActiveRecord uses a single connection to do this instead of creating multiple connections for each entry.
  All I need is a way to check records existence in a single connection with a maximum performance with lower overhead on both sides Mysql and Rails ?? 
  Any suggestions for this please..   </p>