Sql Query Need

Hi All,

Pls help me to prepare sql query as per below requirement:

I have created below records through application.

                                  Effective_Start_date                   Effective_end_date

Contingent Worker   01-Jan-2012                                   09-Jan-2012

Employee                 10-Jan-2012                                 31-Dec-4712

User will pass two parameters like start_date and end_date. Sql code work in such a way that,

Start_date : 01-Jan-2012

end_date : 08-jan-2012       Sql code return one record(Contingent worker)

start_date: 11-Jan-2012

End_date : 30-Jan-2012  return one record like Employee

Start_date:01-Jan-2012

End_date:30-Jan-2012  Display two records (Contingent worker and EMployee).

Need query accordingly.