create table t1 (a int);
alter table mysql.column_stats rename to mysql.column_stats1;
flush tables;
alter table t1 change a b varchar(100);
show create table t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `b` varchar(100) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
alter table mysql.column_stats1 rename to mysql.column_stats;
drop table t1;