Return wrong result when UPDATE's assignment_list has subquery

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

CREATE TABLE `users` (
  `id` bigint(20) unsigned NOT NULL,
  `name` longtext DEFAULT NULL,
  `age` bigint(20) unsigned DEFAULT NULL,
  `company_id` bigint(20) DEFAULT NULL,
  `manager_id` bigint(20) unsigned DEFAULT NULL,
  `active` tinyint(1) DEFAULT NULL,
  `created_at` datetime(3) DEFAULT NULL,
  `updated_at` datetime(3) DEFAULT NULL,
  `deleted_at` datetime(3) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `idx_users_deleted_at` (`deleted_at`)
);
insert into users(id, company_id, name, updated_at) values(239, 15, 'Company 2 id 15', '2021-03-01 12:12:12.987');
create table companies(id bigint primary key, name longtext default null);
insert into companies values(14, 'Company 1 id 14');
insert into companies values(15, 'Company 2 id 15');
UPDATE `users` SET `company_id`=14,`name`=(SELECT `name` FROM `companies` WHERE companies.id = users.company_id),`updated_at`='2021-04-27 10:28:31.459' WHERE `id` = 239;

2. What did you expect to see? (Required)

select * from users;

name is not null

3. What did you see instead (Required)

but it is null

4. What is your TiDB version? (Required)

master branch

[ti-srebot]

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