text: create table t(a char(10));
  create index idx1 on t(lower(a) asc);
  create index idx2 on t(lower(a) desc);
  show index in t;
  drop table t;
  create table t(a int, key idx1(log10(a) asc),index idx2 (log10(a) desc));
  show index in t;
  drop table t;
  create table t(a date);
  alter table t add index idx1(year(a) asc),add key idx2(year(a) desc);
  show index in t;
  drop table t;