使用Inner Join和Where提高MySQL Update查询的速度

Question

我有一个运行缓慢的更新查询，想看看我是否可以提高性能

这是查询

update appmaster a
  INNER JOIN appid b ON a.activity = b.activity
  SET a.activity_id = b.activity_id
  WHERE a.activity_id IS null 

appmaster包含大约9百万条记录，但不到100万条记录的activity_id为空

appid包含171,000条记录

我尝试为这两个表设置活动索引，但似乎没有帮助。 我会在appmaster activity_id上设置一个索引，因为这是我的where条件，但这是值im设置。

有什么想法吗？

appmaster table

CREATE TABLE appfiltration.appmaster (
  id int(11) NOT NULL AUTO_INCREMENT,
  name varchar(75) DEFAULT NULL,
  activity varchar(150) NOT NULL,
  class varchar(150) NOT NULL,
  device varchar(60) NOT NULL,
  version varchar(60) DEFAULT NULL,
  theme varchar(50) DEFAULT NULL,
  upload_date date DEFAULT NULL,
  activity_id int(11) DEFAULT NULL,
  PRIMARY KEY (id),
  INDEX idx_activity (activity)
)
ENGINE = INNODB
AUTO_INCREMENT = 9457807
AVG_ROW_LENGTH = 136
CHARACTER SET utf8
COLLATE utf8_unicode_ci;

appid table

CREATE TABLE appfiltration.appid (
  activity_id int(11) NOT NULL AUTO_INCREMENT,
  activity varchar(200) NOT NULL,
  name varchar(50) DEFAULT NULL,
  result int(11) NOT NULL DEFAULT 0,
  change1 float DEFAULT NULL,
  result_last int(11) NOT NULL DEFAULT 0,
  change2 float DEFAULT NULL,
  result_last2 int(11) NOT NULL DEFAULT 0,
  PRIMARY KEY (activity_id, activity)
)
ENGINE = INNODB
AUTO_INCREMENT = 251064
AVG_ROW_LENGTH = 63
CHARACTER SET utf8
COLLATE utf8_unicode_ci;

结果来自

EXPLAIN SELECT a.activity_id, b.activity_id 
FROM appmaster a 
JOIN appid b ON a.activity = b.activity 
WHERE a.activity_id IS NULL