SQL & PL/SQL

Hello,
I've need of writing the following statement as query or procedure within SSRS 2008(SQL Server Reporting Services 2008) to query Oracle data.

IF :PARAMETER1 = 1
SELECT A1,B1,C1 FROM TABLE1
INNER JOIN TABLE2 ON TABLE2.X = TABLE1.X
INNER JOIN TABLE3 ON TABLE3.Y = TABLE1.Y
WHERE TABLE1.FIELD1 = :PARAMETER1
ELSE IF :PARAMETER1 = 0
SELECT A1,B1,C1 FROM TABLE1
INNER JOIN TABLE2 ON TABLE2.X = TABLE1.X
WHERE TABLE1.FIELD1 = :PARAMETER1

Can someone please help since I am trying to write query with IF ELSE statement or block from SSRS 2008?

Brief scenario - I'm trying to query data from Oracle db by using Oracle data source connection(11g client) from SSRS 2008 to display on SSRS report.

Thanks,
JS.