create table t1 (
col1 varchar(32), 
col2 varchar(32), 
key(col1),
key(col2)
) collate utf8mb3_general_ci;
insert into t1
select 
concat('A-', seq),
concat('A-', seq)
from seq_1_to_100;
set
@tmp_ot= @@optimizer_trace,
@tmp_os=@@optimizer_switch,
optimizer_switch='sargable_casefold=on',
optimizer_trace=1;
explain select * from t1 where 'abc'=upper(col1);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	col1	col1	99	const	1	Using index condition
select 
json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
from information_schema.optimizer_trace;
JS
[
    {
        "before": "'abc' = ucase(t1.col1)",
        "after": "'abc' = t1.col1"
    }
]
explain select * from t1 where ucase(col2)=upper(col1);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
select 
json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
from information_schema.optimizer_trace;
JS
[
    {
        "before": "ucase(t1.col2) = ucase(t1.col1)",
        "after": "t1.col2 = t1.col1"
    }
]
explain
select * from t1 where upper(col1) IN ('A-3','A-4','a-5');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	col1	col1	99	NULL	3	Using index condition
# Will show the rewrite:
select 
json_detailed(json_extract(trace, '$**.sargable_casefold_removal')) as JS
from information_schema.optimizer_trace;
JS
[
    {
        "before": "ucase(t1.col1) in ('A-3','A-4','a-5')",
        "after": "t1.col1 in ('A-3','A-4','a-5')"
    }
]
set 
optimizer_trace=@tmp_ot,
optimizer_switch=@tmp_os;
drop table t1;