Mysql：如何找到表A中所有不在表B中的内存表

Question

我有临时内存表A和B.每个包含1列整数值 我需要找到A中的所有值，但是不在B.

问题是，它的速度很慢，因为（我认为）内存表使用散列而不是有序的键。

如何有效地执行它？目前我使用 SELECT VAL FROM TABLEA其中val NOT IN（SELECT VAL FROM tableB的）

每个表的定义： CREATE TABLE表A（VAL INT，PRIMARY KEY使用HASH（VAL））ENGINE = MEMORY;

Answer 1

select 
a.val 
from 
tableA a 
left outer join tableB b on a.val = b.val 
where 
b.val is null; 

在250K行一些额外的测试表明，没有太多的他们之间：

call load_test_data(); 

call test_memory_tables_hash(); -- 0:00:00.597 
call test_memory_tables_hash(); -- 0:00:00.362 


call load_test_data(); 

call test_memory_tables_btree(); -- 0:00:00.460 
call test_memory_tables_btree(); -- 0:00:00.429 

完整的测试脚本：

drop table if exists tableA; 
create table tableA 
(
val int unsigned not null primary key 
) 
engine=innodb; 

drop table if exists tableB; 
create table tableB 
(
val int unsigned not null primary key 
) 
engine=innodb; 


drop procedure if exists load_test_data; 

delimiter # 

create procedure load_test_data() 
proc_main:begin 

declare i int unsigned default 0; 
declare rnd int unsigned default 0; 
declare max int unsigned default 250000; 

    truncate table tableA; 
    truncate table tableB; 

    set autocommit = 0; 

    while i < max do 
    if i % 2 = 0 then insert into tableA values (i); end if; 
    if i % 3 = 0 then insert into tableB values (i); end if; 
    set i = i+1; 
    end while; 

    commit; 

end proc_main # 

delimiter ; 

drop procedure if exists test_memory_tables_hash; 

delimiter # 

create procedure test_memory_tables_hash() 
proc_main:begin 

create temporary table mem_tableA 
(
    val int unsigned not null, index using hash(val) 
) 
engine=memory select val from tableA; 

create temporary table mem_tableB 
(
    val int unsigned not null, index using hash(val) 
) 
engine=memory; 

insert into mem_tableA select val from tableA; 
insert into mem_tableB select val from tableB; 

select 
a.val 
from 
mem_tableA a 
left outer join mem_tableB b on a.val = b.val 
where 
b.val is null 
order by 
a.val desc 
limit 64; 

drop temporary table if exists mem_tableA; 
drop temporary table if exists mem_tableB; 

end proc_main # 

delimiter ; 

delimiter ; 

drop procedure if exists test_memory_tables_btree; 

delimiter # 

create procedure test_memory_tables_btree() 
proc_main:begin 

create temporary table mem_tableA 
(
    val int unsigned not null, index using btree(val) 
) 
engine=memory select val from tableA; 

create temporary table mem_tableB 
(
    val int unsigned not null, index using btree(val) 
) 
engine=memory; 

insert into mem_tableA select val from tableA; 
insert into mem_tableB select val from tableB; 

select 
a.val 
from 
mem_tableA a 
left outer join mem_tableB b on a.val = b.val 
where 
b.val is null 
order by 
a.val desc 
limit 64; 

drop temporary table if exists mem_tableA; 
drop temporary table if exists mem_tableB; 

end proc_main # 

delimiter ; 


call load_test_data(); 

call test_memory_tables_hash(); 
-- 0:00:00.597 
call test_memory_tables_hash(); 
-- 0:00:00.362 


call load_test_data(); 

call test_memory_tables_btree(); 
-- 0:00:00.460 
call test_memory_tables_btree(); 
-- 0:00:00.429