with n(str, ori, pos) as (
values ('aa,bb,cc,dd,', 1, posstr('aa,bb,cc,dd,', ','))
union all
select str, pos+1, locate(',', str, pos+1)
from n
where locate(',', str, pos+1)>0)
select str, ori, pos, substr(str, ori, pos-ori) as result from n order by pos desc fetch first 1 rows only;
//其实我只是要取一个字符串中用','分割的最后一段。。。