drop table if exists t;
Warnings:
Note	1051	Unknown table 'test.t'
create table t (id int, x char(2), primary key (id), unique key (x));
insert into t values (1,'aa'),(2,'ab');
select * from t;
id	x
1	aa
2	ab
alter table t modify x char(1);
ERROR 01000: Data truncated for column 'x' at row 1
select * from t;
id	x
1	aa
2	ab
drop table t;
