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|
#
# MDEV-30877: Output cardinality for derived table ignores GROUP BY
#
create table t1 (
groups_20 int,
groups_20_2 int,
b int,
index (groups_20)
);
insert into t1 select seq/1000, seq/1000, seq from seq_1_to_20000;
create table t2 (a int, b int, index(a));
insert into t2 select seq, seq from seq_1_to_10;
analyze table t1 persistent for all;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status Table is already up to date
set optimizer_trace=1;
# Case 1: one indexed column
explain
select *
from
t2,
(select count(*) cnt, groups_20 from t1
group by groups_20) TBL
where
1;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 20 Using join buffer (flat, BNL join)
2 DERIVED t1 index NULL groups_20 5 NULL 20000 Using index
select
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
from
information_schema.optimizer_trace;
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
[
{
"join_output_cardinality": 20000,
"estimation":
[
{
"table": "t1",
"steps":
[
{
"index_name": "groups_20",
"cardinality": 20.99999895
}
],
"cardinality": 20.99999895
}
],
"post_group_cardinality": 20.99999895
}
]
# Case 2: one non- indexed column
explain
select *
from
t2,
(select count(*) cnt, groups_20_2 from t1
group by groups_20_2) TBL
where
1;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 20 Using join buffer (flat, BNL join)
2 DERIVED t1 ALL NULL NULL NULL NULL 20000 Using temporary; Using filesort
select
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
from
information_schema.optimizer_trace;
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
[
{
"join_output_cardinality": 20000,
"estimation":
[
{
"table": "t1",
"steps":
[
{
"column": "groups_20_2",
"cardinality": 20.99999895
}
],
"cardinality": 20.99999895
}
],
"post_group_cardinality": 20.99999895
}
]
# Case 4: one indexed column, multiple tables
create table t3(c int);
insert into t3 select seq from seq_1_to_10;
explain
select *
from
t2,
(select count(*) cnt, groups_20 from t1,t3
group by groups_20) TBL;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 20 Using join buffer (flat, BNL join)
2 DERIVED t3 ALL NULL NULL NULL NULL 10 Using temporary; Using filesort
2 DERIVED t1 index NULL groups_20 5 NULL 20000 Using index; Using join buffer (flat, BNL join)
select
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
from
information_schema.optimizer_trace;
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
[
{
"join_output_cardinality": 200000,
"estimation":
[
{
"table": "t1",
"steps":
[
{
"index_name": "groups_20",
"cardinality": 20.99999895
}
],
"cardinality": 20.99999895
}
],
"post_group_cardinality": 20.99999895
}
]
# Case 5: group by two tables
explain
select *
from
t2,
(select count(*) cnt, groups_20 from t1,t3
group by groups_20, t3.c) TBL;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 209 Using join buffer (flat, BNL join)
2 DERIVED t3 ALL NULL NULL NULL NULL 10 Using temporary; Using filesort
2 DERIVED t1 index NULL groups_20 5 NULL 20000 Using index; Using join buffer (flat, BNL join)
select
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
from
information_schema.optimizer_trace;
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
[
{
"join_output_cardinality": 200000,
"estimation":
[
{
"table": "t1",
"steps":
[
{
"index_name": "groups_20",
"cardinality": 20.99999895
}
],
"cardinality": 20.99999895
},
{
"table": "t3",
"steps":
[],
"cardinality": 10
}
],
"post_group_cardinality": 209.9999895
}
]
# Now, without an index
explain
select *
from
t2,
(select count(*) cnt, groups_20 from t1 use index(),t3 group by groups_20) TBL;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY <derived2> ALL NULL NULL NULL NULL 20 Using join buffer (flat, BNL join)
2 DERIVED t3 ALL NULL NULL NULL NULL 10 Using temporary; Using filesort
2 DERIVED t1 ALL NULL NULL NULL NULL 20000 Using join buffer (flat, BNL join)
select
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
from
information_schema.optimizer_trace;
json_detailed(json_extract(trace, '$**.materialized_output_cardinality'))
[
{
"join_output_cardinality": 200000,
"estimation":
[
{
"table": "t1",
"steps":
[
{
"column": "groups_20",
"cardinality": 20.99999895
}
],
"cardinality": 20.99999895
}
],
"post_group_cardinality": 20.99999895
}
]
set optimizer_trace=default;
drop table t1, t2, t3;
|
