思路：根据字符串拼接 和  字符的先后顺序作为条件

sql：

select CONCAT(a.name,b.name)
from TT a,TT b
where  a.name != b.name and ascii(a.name) < ascii(b.name)
ORDER BY a.name,b.name

函数说明：CONCAT()：sql字符串拼接 ascii():编码