mariadb使用with子句改写性能提升5倍

几个月前，我们有个产品的开发反馈了个问题，说有个组织结构的查询很慢，几千行的复杂关联需要1秒钟，表示太慢了，原语句如下：

SELECT
  org.org_id,
  org.dimension,
  org.org_code,
  org.org_name,
  org.parent_id,
  org.manage_id,
  org.org_cate,
  org.org_level,
  org.org_order,
  org.org_path,
  org.position_code,
  org.ext_id,
  org.remark,
  pos.position_name,
  parent.org_code AS parent_code,
  parent.org_name AS parent_name,
  manage.org_code AS manage_code,
  manage.org_name AS manage_name,
  org. STATUS
FROM
  tsys_organization org
LEFT JOIN tsys_position pos ON org.position_code = pos.position_code
LEFT JOIN tsys_organization parent ON org.parent_id = parent.org_id
LEFT JOIN tsys_organization manage ON org.manage_id = manage.org_id
WHERE 
  org.org_id IN(
    SELECT
      org.org_id
    FROM
      tsys_organization org
    JOIN tsys_user us ON us.user_id ='admin'
    
    UNION
      SELECT
        ou.org_id
      FROM
        tsys_org_user ou
      WHERE
        user_id ='admin'
      UNION
        SELECT
          org.org_id
        FROM
          tsys_organization org
        JOIN pos_user_view po ON po.user_id ='admin'
  )
AND org. STATUS = 0
ORDER BY
  org.org_order

够复杂的，看了下执行计划，确实有个子句没有物化导致i/o访问次数下不来，于是对该子查询使用with重写如下：

with a as (
    SELECT
      org2.org_id
    FROM
      tsys_organization org2
    JOIN tsys_user us ON us.user_id ='admin'
    
    UNION all
      SELECT
        ou.org_id
      FROM
        tsys_org_user ou
      WHERE
        user_id ='admin'
      UNION all
        SELECT
          org1.org_id
        FROM
          tsys_organization org1
        JOIN pos_user_view po ON po.user_id ='admin'
  )
SELECT
  org.org_id,
  org.dimension,
  org.org_code,
  org.org_name,
  org.parent_id,
  org.manage_id,
  org.org_cate,
  org.org_level,
  org.org_order,
  org.org_path,
  org.position_code,
  org.ext_id,
  org.remark,
  pos.position_name,
  parent.org_code AS parent_code,
  parent.org_name AS parent_name,
  manage.org_code AS manage_code,
  manage.org_name AS manage_name,
  org. STATUS
FROM
  tsys_organization org
LEFT JOIN tsys_position pos ON org.position_code = pos.position_code
LEFT JOIN tsys_organization parent ON org.parent_id = parent.org_id
LEFT JOIN tsys_organization manage ON org.manage_id = manage.org_id
WHERE 
  org.org_id IN (select org_id from a)
AND org. STATUS = 0
ORDER BY
  org.org_order

因为mariadb的with子句会强制物化为临时表，改写后，0.2秒执行完成（oracle 12.2开始也支持强制，在此之前需要加materialized提示）。