All about uuid


hello everyone, i build this app using php and mysql and i have a problem with uuid, this my question.

  1. can you tell me everything about uuid?
  2. how can i generate uuid for sending, checking report, or deleting message using php and mysql?
  3. i see the uuid from my phone is change and the SMS in my database to be duplicate, does the uuid is change every moment?
  4. if the uuid from my phone is change, can i validate the uuid from phone with uuid from my database?
  5. im sorry about my english, i dont speak english well, thanks