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Slow database query optimization

2022-07-07 00:47:00 【Sun Zhongming】

You can try to create nested subqueries first , Divide data into small-scale

original

select
  s.school_id,
  s.school_name,
  sum(
    case
      when o.role = 'student' then 1
      else 0
    end
  ) as stu_num
from
  t_school as s 
  left join t_organization as o on s.school_id = o.school_id
 
group by
  s.school_id,
  s.school_name,


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Replace

select
  s.school_id,
  s.school_name,
  sum(
    case
      when o.role = 'student' then 1
      else 0
    end
  ) as stu_num
from
  t_school as s
  left join (
    select
      school_id sum(
        case
          when o.role = 'student' then 1
          else 0
        end
      ) as stu_num
    from
      t_organization
  ) as o on s.school_id = o.school_id
group by
  s.school_id,
  s.school_name,


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原网站

版权声明
本文为[Sun Zhongming]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/02/202202130947247450.html

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Slow database query optimization

original

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