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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%'; Variable_name Value Created_tmp_disk_tables 0 Created_tmp_files 0 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%'; Variable_name Value Created_tmp_disk_tables 0 Created_tmp_files 0 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%'; Variable_name Value Created_tmp_disk_tables 0 Created_tmp_files 0 Created_tmp_tables 2 drop table t3; 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%'; Variable_name Value Created_tmp_disk_tables 0 Created_tmp_files 0 Created_tmp_tables 1 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%'; Variable_name Value Created_tmp_disk_tables 0 Created_tmp_files 0 Created_tmp_tables 0