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create table t2 (a int);
insert into t2 values (1),(2),(3);
create view v2 as select a from t2;
flush status;
select * from v2;
a
1
2
3
show status like '%Created_tmp_tables%';
Variable_name Value
Created_tmp_tables 0
explain select * from v2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3
select * from (select * from t2) T1;
a
1
2
3
show status like '%Created_tmp_tables%';
Variable_name Value
Created_tmp_tables 0
explain select * from (select * from t2) T1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3
drop view v2;
drop table t2;
CREATE TABLE t1(a int);
INSERT INTO t1 values(1),(2);
CREATE TABLE t2(a int);
INSERT INTO t2 values(1),(2);
EXPLAIN SELECT * FROM t1 WHERE a IN (SELECT * FROM t2 GROUP BY a HAVING a > 1);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 2 Using where
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 test.t1.a 1
2 MATERIALIZED t2 ALL NULL NULL NULL NULL 2 Using where; Using temporary
truncate table performance_schema.events_statements_history_long;
flush status;
CREATE TABLE t3 SELECT * FROM t1 WHERE a IN (SELECT * FROM t2 GROUP BY a HAVING a > 1);
# Performance schema should be the same as "Created_tmp_tables" variable below
select sum(created_tmp_tables) from performance_schema.events_statements_history_long;
sum(created_tmp_tables)
2
show status like '%Created_tmp_tables%';
Variable_name Value
Created_tmp_tables 2
drop table t3;
set @@optimizer_switch="firstmatch=off";
EXPLAIN SELECT * FROM t1 WHERE a IN (SELECT * FROM t2 GROUP BY a);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 2
1 PRIMARY <subquery2> eq_ref distinct_key distinct_key 4 func 1
2 MATERIALIZED t2 ALL NULL NULL NULL NULL 2
truncate table performance_schema.events_statements_history_long;
flush status;
CREATE TABLE t3 SELECT * FROM t1 WHERE a IN (SELECT * FROM t2 GROUP BY a);
# Performance schema should be the same as "Created_tmp_tables" variable below
select sum(created_tmp_tables) from performance_schema.events_statements_history_long;
sum(created_tmp_tables)
1
show status like '%Created_tmp_tables%';
Variable_name Value
Created_tmp_tables 1
set @@optimizer_switch=default;
drop table t1,t2,t3;
truncate table performance_schema.events_statements_history_long;
flush status;
# Performance schema should be the same as "Created_tmp_tables" variable below
select sum(created_tmp_tables) from performance_schema.events_statements_history_long;
sum(created_tmp_tables)
0
show status like '%Created_tmp_tables%';
Variable_name Value
Created_tmp_tables 0
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