MS-SQL to PostgreSql

hi,
i am trying to convert this mssql store procedure to postgresql function but it is not giving me the desired output ,this function is returning a table and you dont need to worry about what it is returning all i concern the body part of the function how to transform the ms-sql code into postgresql code,  i shall be very thankful  if some one convert this procedure into function, 

ALTER PROCEDURE [dbo].[sp_GetSitesByTFID]
@UserDataDetailId varchar(50), 
@KBId  varchar(50),
@bpOverlap varchar(50),
@Chr varchar(50),
@CentreDistance varchar(50)='',
@TotalMatched varchar(50) output
AS
BEGIN

DECLARE @sql nvarchar(500);

if (@CentreDistance='')
set @CentreDistance = 1
set @sql = 'select Chr_U, Start_U, End_U, RegionSize_U, Chr_KB, Start_KB, End_KB, RegionSize_KB, '
set @sql += ' bpOverlap, CentreDistance from vwChrCompareSiteswhere UserDataDetailId=' + @UserDataDetailId  
set @sql += ' and bpOverlap>=' + @bpOverlap 
set @sql += ' AND KBId=' + @KBId
if @Chr<>'All' and ISNULL(@Chr,'')<>''
set @sql += ' AND Chr_U=''' + @Chr  +''''
if (@CentreDistance<>'') 
set @sql += ' AND (CentreDistance<=' + @CentreDistance + ' or ' + @CentreDistance + '=1) '
set @sql += ' Order by  Chr_U, Start_U'

exec(@sql)
set @TotalMatched = @@ROWCOUNT
END