1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
|
select FILE_NAME, EVENT_NAME from performance_schema.file_instances
limit 1
into @fname, @ename;
====================================================================
Testing index for columns FILE_NAME
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where FILE_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 count(*)
from performance_schema.file_instances
where FILE_NAME > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL ALL PRIMARY NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where FILE_NAME < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL ALL PRIMARY NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where FILE_NAME = @fname;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL const PRIMARY PRIMARY 2050 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.file_instances
where FILE_NAME = @fname;
count(*)
#
OK: handler_read_key incremented
====================================================================
Testing index for columns EVENT_NAME
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where EVENT_NAME = "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL ref EVENT_NAME EVENT_NAME 514 const # 100.00 NULL
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where EVENT_NAME > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL ALL EVENT_NAME NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where EVENT_NAME < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL ALL EVENT_NAME NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.file_instances
where EVENT_NAME = @ename;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE file_instances NULL ref EVENT_NAME EVENT_NAME 514 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.file_instances
where EVENT_NAME = @ename;
count(*)
#
OK: handler_read_key incremented
|
