替代NOT IN在MySQL上

Question

我有一个问题

SELECT DISTINCT phoneNum 
FROM `Transaction_Register` 
WHERE phoneNum NOT IN (SELECT phoneNum FROM `Subscription`) 
LIMIT 0 , 1000000

执行b/c Transaction_Register表需要太多时间有数百万条记录是否有任何上述查询的替代方案我会感激你们,如果有的话.

Answer 1

另一种方法是使用LEFT JOIN:

select distinct t.phoneNum
from Transaction_Register t
left join Subscription s
  on t.phoneNum = s.phoneNum
where s.phoneNum is null
LIMIT 0 , 1000000;

请参阅SQL Fiddle with Demo

Answer 2

我怀疑是否LEFT JOIN真的比NOT IN. 我只是用下表结构进行了一些测试（如果我错了，请纠正我）：

account (id, ....)   [42,884 rows, index by id]
play (account_id, playdate, ...)   [61,737 rows, index by account_id]

(1) 查询 LEFT JOIN

SELECT * FROM
account LEFT JOIN play ON account.id = play.account_id
WHERE play.account_id IS NULL

(2) 查询 NOT IN

SELECT * FROM
account WHERE
account.id NOT IN (SELECT play.account_id FROM play)

使用 LIMIT 0 进行速度测试，...

LIMIT 0,->   100      150      200      250
-------------------------------------------------------------------------
LEFT         3.213s   4.477s   5.881s   7.472s
NOT EXIST    2.200s   3.261s   4.320s   5.647s
--------------------------------------------------------------------------
Difference   1.013s   1.216s   1.560s   1.825s

随着我增加限制，差异越来越大

和 EXPLAIN

(1) 查询 LEFT JOIN

SELECT_TYPE   TABLE      TYPE   ROWS    EXTRA
-------------------------------------------------
SIMPLE         account   ALL    42,884
SIMPLE         play      ALL    61,737  Using where; not exists

(2) 查询 NOT IN

SELECT_TYPE          TABLE      TYPE   ROWS   EXTRA
-------------------------------------------------
SIMPLE               account   ALL    42,884  Using where
DEPENDENT SUBQUERY   play      INDEX  61,737  Using where; Using index

似乎 LEFT JOIN 没有使用索引

逻辑

(1) 查询 LEFT JOIN

account 和 play 之间的 LEFT JOIN 后将产生 42,884 * 61,737 = 2,647,529,508 行。然后检查这些行上的 play.account_id 是否为 NULL。

(2) 查询 NOT IN

二分搜索采用 log2(N) 来表示项目存在。这意味着 42,884 * log2(61,737) = 686,144 步