mysql的not in 导致查询无结果原因

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错误sql

delete
from
  company_info 
where id NOT in
  (SELECT 
      company_info_ID 
    FROM
      USER);

因为null的原因，导致出现子查询的结果为空。

正确的写法是

-- 清除重复的不可用的公司信息    
delete
from
  company_info 
where id NOT in
  (SELECT 
      company_info_ID 
    FROM
      USER
      where company_info_ID is not null);