create database explain_test_db;
create table explain_test_db.t1 (c int);
insert into explain_test_db.t1 values ('1');
truncate table performance_schema.events_waits_history;
# Connection 1
select connection_id() into @conid;
select * from explain_test_db.t1;
c
1
# Default connection

====================================================================
Testing index for columns THREAD_ID, EVENT_ID
====================================================================
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	ref	PRIMARY	PRIMARY	8	const	#	100.00	Using where
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID > "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	ALL	PRIMARY	NULL	NULL	NULL	#	33.33	Using where
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID < "2";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	ALL	PRIMARY	NULL	NULL	NULL	#	33.33	Using where
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = @tid;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	ref	PRIMARY	PRIMARY	8	const	#	100.00	Using where
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = "impossible"
    and EVENT_ID = "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 END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = @tid
and EVENT_ID = "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 END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = @tid
and EVENT_ID > "impossible";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	ref	PRIMARY	PRIMARY	8	const	#	33.33	Using where
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = @tid
and EVENT_ID < "2";
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	ref	PRIMARY	PRIMARY	8	const	#	33.33	Using where
############ Explain for Query ####################################
explain select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = @tid
and EVENT_ID = @eid;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	events_waits_history	NULL	const	PRIMARY	PRIMARY	16	const,const	#	100.00	NULL
############# Explain End #########################################
flush status;
select END_EVENT_ID
from performance_schema.events_waits_history
where THREAD_ID = @tid
and EVENT_ID = @eid;
END_EVENT_ID
#
OK: handler_read_key incremented
drop table explain_test_db.t1;
drop database explain_test_db;