declare @T datetime;
set @T=getdate();
SELECT COUNT(*) AS Expr1
FROM sys.sysprocesses AS a INNER JOIN
random_data AS b ON a.waittype =dbo.fn_shit(b.col3)
where b.col1< 10000 ;
print 'Elapsed:';
print datediff(ms,@T,getdate());

    [Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = true, DataAccess = Microsoft.SqlServer.Server.DataAccessKind.None)]
    public static SqlString fn_shit_clr(SqlString str)
    {
        if (str.IsNull) return str;
        return str + "shit";
        
    }

  select count(*) from all_objects a, tst b
where a.owner=fn_shit(b.col1) ;

  COUNT(*)
----------
         0

Elapsed: 00:00:13.12
SQL> /

  COUNT(*)
----------
         0

Elapsed: 00:00:13.02
SQL> /

  COUNT(*)
----------
         0

Elapsed: 00:00:13.34
select count(*) from all_objects a, tst b
  2  where a.owner=fn_shit(b.col1) and id<10000;

  COUNT(*)
----------
         0

Elapsed: 00:00:01.09
SQL> /

  COUNT(*)
----------
         0

Elapsed: 00:00:01.04
SQL> /

  COUNT(*)
----------
         0

Elapsed: 00:00:01.04