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select OBJECT_INSTANCE_BEGIN, NAME from performance_schema.cond_instances
limit 1
into @oib, @name;
====================================================================
Testing index for columns OBJECT_INSTANCE_BEGIN
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where OBJECT_INSTANCE_BEGIN = "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 count(*)
from performance_schema.cond_instances
where OBJECT_INSTANCE_BEGIN > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL ALL PRIMARY NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where OBJECT_INSTANCE_BEGIN < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL ALL PRIMARY NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where OBJECT_INSTANCE_BEGIN = @oib;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL const PRIMARY PRIMARY 8 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.cond_instances
where OBJECT_INSTANCE_BEGIN = @oib;
count(*)
#
OK: handler_read_key incremented
====================================================================
Testing index for columns NAME
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where NAME = "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL ref NAME NAME 514 const # 100.00 NULL
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where NAME > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL ALL NAME NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where NAME < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL ALL NAME NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.cond_instances
where NAME = @name;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE cond_instances NULL ref NAME NAME 514 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.cond_instances
where NAME = @name;
count(*)
#
OK: handler_read_key incremented
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