Ruby on Rails

I have set my float id's. I have a Rails 3.0 app and using a MySQL database. It seemed to work fine on a Postgres database. 

Here is my problem:

irb(main):033:0> Patient.first

  Patient Load (1.3ms)  SELECT `patients`.* FROM `patients` LIMIT 1

=> #<Patient pid: 29312000.0, created_at: "2014-04-25 19:05:10", updated_at: "2014-04-25 19:05:10", race: "WHITE", ethnicity: "NOT HISPANIC", age: 47>

irb(main):034:0> Patient.find_by_pid(Patient.first.pid)

  Patient Load (1.1ms)  SELECT `patients`.* FROM `patients` LIMIT 1

  Patient Load (346.1ms)  SELECT `patients`.* FROM `patients` WHERE `patients`.`pid` = 29312000.0 LIMIT 1

=> nil

Basically, I can not use where I have used Float as a part of an Active Record Query. Another similar problem on another model. 

irb(main):035:0> Lab.first

  Lab Load (1.3ms)  SELECT `labs`.* FROM `labs` LIMIT 1

=> #<Lab id: 1, patient_id: 29312000.0, code_id: 1, lab_date: "2010-11-29", value: 51, age: 47, created_at: "2014-04-25 19:05:10", updated_at: "2014-04-25 19:05:10", difference: 12, report_id: 2432930000.0>

irb(main):036:0> Lab.find_by_patient_id(Lab.first.patient_id)

  Lab Load (1.2ms)  SELECT `labs`.* FROM `labs` LIMIT 1

  Lab Load (341.4ms)  SELECT `labs`.* FROM `labs` WHERE `labs`.`patient_id` = 29312000.0 LIMIT 1