create user foo@localhost;
grant ALL on *.* to foo@localhost;

====================================================================
Testing index for columns HOST, USER, EVENT_NAME
====================================================================
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ALL	NULL	NULL	NULL	NULL	#	10.00	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST > "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ALL	NULL	NULL	NULL	NULL	#	33.33	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST < "2";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ALL	NULL	NULL	NULL	NULL	#	33.33	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ALL	NULL	NULL	NULL	NULL	#	10.00	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "impossible"
    and USER = "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ref	ACCOUNT	ACCOUNT	385	const,const	#	100.00	NULL
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ref	ACCOUNT	ACCOUNT	385	const,const	#	100.00	NULL
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER > "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ALL	ACCOUNT	NULL	NULL	NULL	#	3.33	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER < "2";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ALL	ACCOUNT	NULL	NULL	NULL	#	3.33	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "foo";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ref	ACCOUNT	ACCOUNT	385	const,const	#	100.00	NULL
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "impossible"
    and USER = "impossible"
    and EVENT_NAME = "impossible";
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	no matching row in const table
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "foo"
and EVENT_NAME = "impossible";
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	no matching row in const table
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "foo"
and EVENT_NAME > "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ref	ACCOUNT	ACCOUNT	385	const,const	#	33.33	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "foo"
and EVENT_NAME < "2";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	ref	ACCOUNT	ACCOUNT	385	const,const	#	33.33	Using where
############ Explain for Query ####################################
explain select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "foo"
and EVENT_NAME = "memory/sql/help";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	memory_summary_by_account_by_event_name	NULL	const	ACCOUNT	ACCOUNT	899	const,const,const	#	100.00	NULL
############# Explain End #########################################
flush status;
select LOW_COUNT_USED
from performance_schema.memory_summary_by_account_by_event_name
where HOST = "localhost"
and USER = "foo"
and EVENT_NAME = "memory/sql/help";
LOW_COUNT_USED
#
OK: handler_read_key incremented
drop user foo@localhost;