Oracle SQL查询的性能调优

Question

有人可以帮我调整这个查询吗？ sqldeveloper返回数据需要1分钟时间。

SELECT
  masterid, notification_id, notification_list, typeid,
  subject, created_at, created_by, approver, sequence_no,
  productid, statusid, updated_by, updated_at, product_list,
  notification_status, template, notification_type, classification
FROM 
( 
  SELECT
    masterid, notification_id, notification_list, typeid, subject,
    approver, created_at, created_by, sequence_no, productid,
    statusid, updated_by, updated_at, product_list, notification_status,
    template, notification_type, classification,
    ROW_NUMBER() OVER(ORDER BY masterid DESC)AS r
  FROM 
  (
    SELECT DISTINCT
      a.masterid         AS masterid,
      a.maxid            AS notification_id,
      notification_list,
      typeid,
      noti.subject       AS subject,
      noti.approver      AS approver,
      noti.created_at    AS created_at,
      noti.created_by    AS created_by,
      noti.sequence_no   AS sequence_no,
      a.productid        AS productid,
      a.statusid         AS statusid,
      noti.updated_by    AS updated_by,
      noti.updated_at    AS updated_at,
      (
        SELECT LISTAGG(p.name,',') WITHIN GROUP(ORDER BY p.id) AS list_noti
        FROM product p
        INNER JOIN notification_product np ON np.product_id = p.id
        WHERE  notification_id = a.maxid
      ) AS product_list,
      (
        SELECT description
        FROM notification_status
        WHERE id = a.statusid
      ) AS notification_status,
      (
        SELECT name
        FROM template
        WHERE id = a.templateid
      ) AS template,
      (
        SELECT description
        FROM notification_type
        WHERE id = a.typeid
      ) AS notification_type,
      (
        SELECT tc.description
        FROM template_classification tc
        INNER JOIN notification nt ON tc.id = nt.classification_id
        WHERE  nt.id = a.maxid
      ) AS classification
    FROM
    (
      SELECT
        nm.id                       AS masterid,
        nm.product_id               AS productid,
        nm.notification_status_id   AS statusid,
        nm.template_id              AS templateid,
        nm.notification_type_id     AS typeid,
        (
          SELECT MAX(id)
          FROM notification
          WHERE notification_master_id = nm.id
        ) AS maxid,
        (
          SELECT LISTAGG(n.id,',') WITHIN GROUP(ORDER BY nf.id) AS list_noti
          FROM notification n
          WHERE notification_master_id = nm.id
        ) AS notification_list
      FROM notification_master nm
      INNER JOIN notification nf ON nm.id = nf.notification_master_id
      WHERE nm.disable = 'N'
      ORDER BY nm.id DESC
    ) a
    INNER JOIN notification noti 
      ON a.maxid = noti.id
      AND 
      (
        (
          (
            TO_DATE('01-jan-1970','dd-MM-YYYY') +
            numtodsinterval(created_at / 1000,'SECOND')
           ) < 
           (current_date + INTERVAL '-21' DAY)
        )
        OR (typeid exists(2,4) AND statusid = 4)
      )
  )
)
WHERE r BETWEEN 11 AND 20

Answer 1

DISTINCT 通常表示查询写得不好。规范化的数据库不包含重复数据，那么您必须使用DISTINCT 删除的重复数据突然来自哪里？很多时候是你自己的查询产生这些。一开始就避免产生重复，这样以后就不需要DISTINCT了。

在您的情况下，您在子查询a 中加入了表notification，但您没有在该子查询中使用它的行；你只能从notification_master_id中选择。

毕竟，您想获得通知大师，获得他们最新的相关通知（首先获取其 ID，然后选择行）。您不需要数百个子查询来实现这一点。

一些旁注：

• 要从template_classification 获取描述，您将再次加入通知表，这不是必需的。
• 子查询 (ORDER BY nm.id DESC) 中的 ORDER BY 是多余的，因为子查询结果按照标准 SQL 未排序。 （Oracle 有时会违反此标准，以便在结果上应用 ROWNUM，但您没有在查询中使用 ROWNUM。）
• 很遗憾您将created_at 存储为一个数字而不是DATE 或TIMESTAMP。这迫使你计算。不过，我认为这对您的查询影响不大，因为您在 OR 条件下使用它。
• CURRENT_DATE 为您提供客户日期。这是很少需要的，因为您从数据库中选择数据，这当然不应该与某些客户的日期相关，而是与它自己的日期相关 SYSDATE。

如果我没记错的话，你的查询可以缩短为：

SELECT
  nm.id                      AS masterid,
  nf.id                      AS notification_id,
  nfagg.notification_list    AS notification_list,
  nm.notification_type_id    AS typeid,
  nf.subject                 AS subject,
  nf.approver                AS approver,
  nf.created_at              AS created_at,
  nf.created_by              AS created_by,
  nf.sequence_no             AS sequence_no,
  nm.product_id              AS productid,
  nm.notification_status_id  AS statusid,
  nf.updated_by              AS updated_by,
  nf.updated_at              AS updated_at,
  (
    SELECT LISTAGG(p.name, ',') WITHIN GROUP (ORDER BY p.id)
    FROM product p
    INNER JOIN notification_product np ON np.product_id = p.id
    WHERE np.notification_id = nf.id
  ) AS product_list,
  (
    SELECT description
    FROM notification_status
    WHERE id = nm.notification_status_id
  ) AS notification_status,
  (
    SELECT name
    FROM template
    WHERE id = nm.template_id
  ) AS template,
  (
    SELECT description
    FROM notification_type
    WHERE id = nm.notification_type_id
  ) AS notification_type,
  (
    SELECT description
    FROM template_classification
    WHERE id = nf.classification_id
  ) AS classification
FROM notification_master nm
INNER JOIN
(
  SELECT
    notification_master_id,
    MAX(id) AS maxid,
    LISTAGG(id,',') WITHIN GROUP (ORDER BY id) AS notification_list
  FROM notification
  GROUP BY notification_master_id
) nfagg ON nfagg.notification_master_id = nm.id
INNER JOIN notification nf
   ON nf.id = nfagg.maxid
  AND
  (
    (
      DATE '1970-01-01' + NUMTODSINTERVAL(nf.created_at / 1000, 'SECOND')
        < CURRENT_DATE + INTERVAL '-21' DAY
    )
    OR (nm.notification_type_id IN (2,4) AND nm.notification_status_id = 4)
  )
WHERE nm.disable = 'N'
ORDER BY nm.id DESC
OFFSET 10 ROWS
FETCH NEXT 10 ROWS ONLY;

如前所述，您可能希望将 CURRENT_DATE 替换为 SYSDATE。

我为查询推荐以下索引：

CREATE INDEX idx1 ON notification_master (disable, id, notification_status_id, notification_type_id);
CREATE INDEX idx2 ON notification (notification_master_id, id, created_at);

关于分页的最后一句话：为了跳过 n 行以获取下一个 n，必须对所有数据执行整个查询，然后对所有结果行进行排序，最后选择其中的 n 个。通常最好记住最后一次获取的 ID，然后在下次执行时只选择 ID 较高的行。