create database explain_test_db;
use explain_test_db;
select 1;
1
1
use test;

====================================================================
Testing index for columns BUCKET_NUMBER
====================================================================
############ Explain for Query ####################################
explain select COUNT_BUCKET 
from performance_schema.events_statements_histogram_global 
where BUCKET_NUMBER = "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_statements_histogram_global	NULL	const	PRIMARY	PRIMARY	4	const	#	100.00	NULL
############ Explain for Query ####################################
explain select COUNT_BUCKET
from performance_schema.events_statements_histogram_global
where BUCKET_NUMBER > "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_statements_histogram_global	NULL	ALL	PRIMARY	NULL	NULL	NULL	#	33.33	Using where
############ Explain for Query ####################################
explain select COUNT_BUCKET
from performance_schema.events_statements_histogram_global
where BUCKET_NUMBER < "2";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_statements_histogram_global	NULL	ALL	PRIMARY	NULL	NULL	NULL	#	33.33	Using where
############ Explain for Query ####################################
explain select COUNT_BUCKET
from performance_schema.events_statements_histogram_global
where BUCKET_NUMBER = 12;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_statements_histogram_global	NULL	const	PRIMARY	PRIMARY	4	const	#	100.00	NULL
############# Explain End #########################################
flush status;
select COUNT_BUCKET
from performance_schema.events_statements_histogram_global
where BUCKET_NUMBER = 12;
COUNT_BUCKET
#
OK: handler_read_key incremented
drop database explain_test_db;