Oracle 性能调优 - 列部分中的迭代表

Question

以下查询需要 220 秒。我想调一下。 查询中主要使用了三个表。两个很大，一个相当小。

表格中的计数：

INST        --14851330 records 
INST_S_INC  --52234424 records
INVES         -- 80000 records

查询：

SELECT 
(
  SELECT CODE
  FROM   CURRENCY CURR
  WHERE  CURR.CURRENCY_ID =
           ( SELECT CURRENCY_ID
             FROM INST  INSTR--14851330 records 
             WHERE INSTR.INVES_ID = INV.INVES_ID
             UNION ALL
             SELECT CURRENCY_ID
             FROM INST_S_INC ISI--52234424 records
             WHERE ISI.INVES_ID = INV.INVES_ID
           )
)
FROM   INVES INV -- 80000 records
WHERE  TRUNC(CREATED_DATETIME) <SYSDATE
ORDER BY CREATED_DATETIME
;--220 secs

我尝试如下重写查询，但现在需要 418 秒。有什么其他的调音方法吗？

SELECT
(
  SELECT CODE
  FROM CURRENCY CURR
  WHERE CURR.CURRENCY_ID =ISI.currency_id
  union all
  SELECT CODE
  FROM CURRENCY CURR
  WHERE CURR.CURRENCY_ID =INSTR.currency_id
) code
FROM   INVES INV
       left outer join (
         select INVES_ID,currency_id from INST
       )  INSTR
       on  INSTR.INVES_ID = INV.INVES_ID
       left outer join (
         select INVES_ID,currency_id from INST_S_INC
       )  ISI
       on  ISI.INVES_ID = INV.INVES_ID
WHERE TRUNC(CREATED_DATETIME) <SYSDATE 
ORDER BY CREATED_DATETIME
;--418 secs

Answer 1

你可以改变：

TRUNC(CREATED_DATETIME) < SYSDATE

收件人：

CREATED_DATETIME < TRUNC( SYSDATE ) + INTERVAL '1' DAY

这将允许您使用CREATED_DATETIME 上的任何索引（而不是必须在TRUNC(CREATED_DATETIME) 上使用基于函数的索引）。

很难解释您的要求，因为您没有描述您要实现的目标或表结构，但您也可以尝试使用 EXISTS 并直接从 CURRENCY 表中选择：

SELECT curr.CODE
FROM   CURRENCY CURR
WHERE  EXISTS (
         SELECT CURRENCY_ID
         FROM   INST
                INNER JOIN
                INVES
                ON ( INST.INVES_ID = INVES.INVES_ID )
         WHERE  INSRT.CURRENCY_ID  = CURR.CURRENCY_ID
         AND    CREATED_DATETIME   < TRUNC( SYSDATE ) + INTERVAL '1' DAY
       )
OR     EXISTS (
         SELECT CURRENCY_ID
         FROM   INST_S_INC ISI
                INNER JOIN
                INVES
                ON ( ISI.INVES_ID = INVES.INVES_ID )
         WHERE  ISI.CURRENCY_ID   = CURR.CURRENCY_ID
         AND    CREATED_DATETIME  < TRUNC( SYSDATE ) + INTERVAL '1' DAY
       )

或者在EXISTS 中使用UNION ALL。

Answer 2

WHERE  TRUNC(CREATED_DATETIME) <SYSDATE

这个过滤器的意义何在？假设您将来不创建基本上定义全表扫描的记录。

在没有解释计划和数据量、偏斜等细节的情况下进行性能调优是一个愚蠢的游戏，但这是我的猜测：

SELECT curr,code
FROM   INVES INV
       left outer join INST
       on  INSTR.INVES_ID = INV.INVES_ID
       left outer join  INST_S_INCISI
       on  ISI.INVES_ID = INV.INVES_ID
left outer join CURRENCY CURR
on CURR.CURRENCY_ID = coalesce (ISI.currency_id, INST.currency_id)
ORDER BY inv.CREATED_DATETIME
;-