SQL：Oracle：優化LEFT外部聯接查詢

Question

我有1個本地表（所有列名與遠程表不同，除了一個）和2個遠程表（具有相同的列名），我需要組合數據。

以下是我使用LEFT OUTER JOIN和UNION編寫的查詢，但性能很慢。

有人可以幫助優化此查詢嗎？

select
"CONTROL_M_SERVER",
"HOST",
CASE
WHEN "AGSTAT" = 'V' THEN 'Available'
WHEN "AGSTAT" = 'U' THEN 'Unavailable'
WHEN "AGSTAT" = 'R' THEN 'Discovering'
ELSE 'Not Defined in Control-M'
END as Agent_Status,
T1.VERSION,
"PORTS",
"MANAGEMENT_IP",
"OPERATING_SYSTEM",
"CLUSTER_ALIAS",
"NODEGROUP",
"APPLICATION_ID",
"DATE_CONFIGURED",
"CONFIGURED_BY"
from "CTMAGENTAUDIT" T1
left outer join (select NODEID,AGSTAT from CMR_NODES@SPDB UNION ALL select NODEID,AGSTAT from CMR_NODES@DEVDB) T2 on T2.NODEID = T1.HOST;

Answer 1

我在查詢中看到的主要問題是CTMAGENTAUDIT和包含union的子查詢之間的最左邊連接。 該子查詢的問題在於，正如所寫，Oracle不可能使用任何索引進行連接。 這意味着Oracle在加入時可能不得不采用較慢的方法，可能是完整掃描。

這里的一種方法是創建一個包含union查詢的物化視圖，然后將其編入索引：

CREATE MATERIALIZED VIEW T2 AS
SELECT NODEID, AGSTAT FROM CMR_NODES@SPDB
UNION ALL
SELECT NODEID, AGSTAT FROM CMR_NODES@DEVDB;

CREATE INDEX mv_node_idx ON T2 (NODEID);

有了這個索引的物化視圖，我希望您的查詢現在可以更好地執行：

SELECT
    CONTROL_M_SERVER,
    HOST,
    CASE WHEN AGSTAT = 'V' THEN 'Available'
         WHEN AGSTAT = 'U' THEN 'Unavailable'
         WHEN AGSTAT = 'R' THEN 'Discovering'
         ELSE 'Not Defined in Control-M' END AS Agent_Status,
    T1.VERSION,
    PORTS,
    MANAGEMENT_IP,
    OPERATING_SYSTEM,
    CLUSTER_ALIAS,
    NODEGROUP,
    APPLICATION_ID,
    DATE_CONFIGURED,
    CONFIGURED_BY
FROM CTMAGENTAUDIT T1
LEFT OUTER JOIN T2
    ON T2.NODEID = T1.HOST;

Answer 2

我會做這樣的事情：

select
"CONTROL_M_SERVER",
"HOST",
CASE
WHEN "AGSTAT" = 'V' THEN 'Available'
WHEN "AGSTAT" = 'U' THEN 'Unavailable'
WHEN "AGSTAT" = 'R' THEN 'Discovering'
ELSE 'Not Defined in Control-M'
END as Agent_Status,
T1.VERSION,
"PORTS",
"MANAGEMENT_IP",
"OPERATING_SYSTEM",
"CLUSTER_ALIAS",
"NODEGROUP",
"APPLICATION_ID",
"DATE_CONFIGURED",
"CONFIGURED_BY",
(select t2.NODEID, t2.AGSTAT from CMR_NODES@SPDB t2 where t1.host = t2.nodeid),  
(select t3.NODEID, t3.AGSTAT from CMR_NODES@DEVDB t3 where T1.HOST = T3.NODEID) from t1;

Answer 3

您的查詢基本上是：

select . . .
from CTMAGENTAUDIT T1 left outer join
     (select NODEID, AGSTAT
      from CMR_NODES@SPDB UNION ALL
      select NODEID, AGSTAT
      from CMR_NODES@DEVDB
     ) T2
     on T2.NODEID = T1.HOST;

假設NODEID / AGSTAT組合在每個CMR_NODE表中都是唯一的，我會將其寫成：

select . . .,
       coalesce(s1.AGSTAT, s2.AGSTAT) as AGSTAT,
       (case coalesce(s1.AGSTAT, s2.AGSTAT) 
            when 'V' then 'Available'
            when 'U' then 'Unavailable'
            when 'R' then 'Discovering'
            else 'Not Defined in Control-M'
        end) as Agent_Status
from CTMAGENTAUDIT T1 left outer join
     CMR_NODES@SPDB s1
     on s1.NODEID = T1.HOST left outer join
     CMR_NODES@DEVDB s2
     on s1.NODEID = T1.HOST

這將至少允許每個表單獨優化 - 這應該有所幫助。

顯然，如果您具有設置跨服務器物化視圖的權限和願望，那么具有物化視圖的解決方案將更快。 物化視圖還存在其他維護問題，特別是如果您有多個此類視圖並假設它們同時更新。