使用order by出错解决方法

使用order by出错
select * from
(select rtrim(ltrim(first_name_srch)) || ' ' || right(rtrim(ltrim(emplid)),3) as ta from ps_names) x
order by ta desc

错误信息

SQL0134N 字符串列,主机变量,常量或函数'TA'使用不当



------解决方案--------------------------------------------------------
select * from (
select rtrim(char( rtrim(ltrim(first_name_srch))||' '||right(rtrim(ltrim(emplid)),3) )) as ta from ps_names
) x
order by ta desc