drop table if exists t1;
create table t1 (t1 char(3) primary key) charset utf8mb4;
insert into t1 values("ABC");
insert into t1 values("ABA");
insert into t1 values("AB%");
select * from t1 where t1="ABC";
t1
ABC
select * from t1 where t1="ABCD";
t1
select * from t1 where t1 like "a_\%";
t1
AB%
describe select * from t1 where t1="ABC";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	NULL	const	PRIMARY	PRIMARY	12	const	1	100.00	Using index
Warnings:
Note	1003	/* select#1 */ select 'ABC' AS `t1` from `test`.`t1` where true
describe select * from t1 where t1="ABCD";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
Warnings:
Note	1003	/* select#1 */ select 'ABC' AS `t1` from `test`.`t1` where false
drop table t1;