Declare @year1 varchar(10)='1998'
Declare @year2 varchar(10)='1999', @Sql nvarchar(200)
Set @Sql ='Select sum(case when year=' + @year1 +' then sales end) [' + @year1 +'],sum(case when year=' + @year2 + ' then sales end) [' + @year2 +'] from salestable'
Exec (@Sql)