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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;
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