create table t1 (f1 int primary key, f2 int, unique key k1(f2)) engine=innodb;
show create table t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `f1` int(11) NOT NULL,
  `f2` int(11) DEFAULT NULL,
  PRIMARY KEY (`f1`),
  UNIQUE KEY `k1` (`f2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
insert into t1(f1, f2) values (1, 10);
insert into t1(f1, f2) values (2, 55);
set debug = '+d,idx_mimic_not_committed';
update t1 set f2 = 55 where f1 = 1;
ERROR 23000: Duplicate entry '55' for key 'k1'
set debug = '-d,idx_mimic_not_committed';
drop table t1;