Question

我继承了这个查询来重建它：

SELECT a.poclcdde,
               a.poclnpol,
               a.poclcdce,
               a.poclcdcl,
               a.poclnuor
          FROM dtpocl a
         WHERE     a.poclcdre = '02'
               AND a.poclxope IN ('01', '02')
               AND a.poclnuor =
                      (SELECT MAX (b.poclnuor)
                         FROM dtpocl b
                        WHERE     b.poclcdde = a.poclcdde
                              AND b.poclnpol = a.poclnpol
                              AND b.poclcdce = a.poclcdce
                              AND b.poclcdre = '02'
                              AND b.poclxope IN ('01', '02')
                              AND NVL (b.poclfecb, 99999999) =
                                     (SELECT MAX (NVL (c.poclfecb, 99999999))
                                        FROM dtpocl c
                                       WHERE     c.poclcdde = b.poclcdde
                                             AND c.poclnpol = b.poclnpol
                                             AND c.poclcdce = b.poclcdce
                                             AND c.poclcdre = '02'
                                             AND c.poclxope IN ('01', '02')))

我有这个解释计划：

Plan hash value: 94095463

--------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name      | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |           |  6293 |   497K|       | 53434   (3)| 00:00:03 |
|   1 |  NESTED LOOPS                |           |       |       |       |            |          |
|   2 |   NESTED LOOPS               |           |  6293 |   497K|       | 53434   (3)| 00:00:03 |
|   3 |    VIEW                      | VW_SQ_2   | 12340 |   626K|       | 41045   (4)| 00:00:02 |
|   4 |     HASH GROUP BY            |           | 12340 |   602K|   792K| 41045   (4)| 00:00:02 |
|*  5 |      HASH JOIN               |           | 12340 |   602K|    47M| 40911   (4)| 00:00:02 |
|   6 |       VIEW                   | VW_SQ_1   |  1555K|    29M|       | 23144   (4)| 00:00:01 |
|   7 |        HASH GROUP BY         |           |  1555K|    40M|    65M| 23144   (4)| 00:00:01 |
|*  8 |         TABLE ACCESS FULL    | DTPOCL    |  1555K|    40M|       | 12793   (4)| 00:00:01 |
|*  9 |       TABLE ACCESS FULL      | DTPOCL    |  1555K|    44M|       | 12801   (4)| 00:00:01 |
|* 10 |    INDEX RANGE SCAN          | PK_DTPOCL |     1 |       |       |     1   (0)| 00:00:01 |
|* 11 |   TABLE ACCESS BY INDEX ROWID| DTPOCL    |     1 |    29 |       |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   5 - access("MAX(NVL(C.POCLFECB,99999999))"=NVL("POCLFECB",'99999999') AND 
              "ITEM_1"="POCLCDDE" AND "ITEM_2"="POCLNPOL" AND "ITEM_3"="POCLCDCE")
   8 - filter("POCLCDRE"='02' AND ("POCLXOPE"='01' OR "POCLXOPE"='02'))
   9 - filter("POCLCDRE"='02' AND ("POCLXOPE"='01' OR "POCLXOPE"='02'))
  10 - access("ITEM_4"="POCLCDDE" AND "ITEM_5"="POCLNPOL" AND "ITEM_6"="POCLCDCE" AND 
              "POCLNUOR"="MAX(B.POCLNUOR)")
  11 - filter("POCLCDRE"='02' AND ("POCLXOPE"='01' OR "POCLXOPE"='02'))

乍一看，我可以想象这是一个错误的查询，因为：为什么我们需要为同一个表执行两个以上的子查询？我需要的是来自dtpocl表（具有此条件a.poclcdre = '02' AND a.poclxope IN ('01', '02')）的所有记录，其最大poclnuor和最大日期poclfecb。

我试图在同一个查询中对两个聚合函数进行分组，如下所示：

SELECT a.poclcdde,
                 a.poclnpol,
                 a.poclcdce,
                 a.poclcdcl,
                 MAX (a.poclnuor),
                 MAX (NVL (a.poclfecb, 99999999))
            FROM dtpocl a
           WHERE a.poclcdre = '02' AND a.poclxope IN ('01', '02')
        GROUP BY a.poclcdde,
                 a.poclnpol,
                 a.poclcdce,
                 a.poclcdcl

但是我得到的记录多于原始查询，成本为25.654。 dtpocl表有3.025.510行。

我们可以采取哪些措施来提高性能和查询可读性？感谢。

Answer 1

您可以使用分析功能查找您感兴趣的poclnuor。

SELECT
  *
FROM
(
  SELECT
    dtpocl.*,
    MAX(poclnuor)
      KEEP (DENSE_RANK FIRST ORDER BY poclfecb DESC NULLS FIRST)
      OVER (PARTITION BY poclcdde, poclnpol, poclcdce)
        AS target_poclnuor
  FROM
    dtpocl
  WHERE
        poclcdre = '02'
    AND poclxope IN ('01', '02')
)
  sorted
WHERE
  poclnuor = target_poclnuor

我从这里得到了语法...... https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions056.htm

您可能想要一个涵盖(poclcdde, poclnpol, poclcdce, poclfecb DESC, poclnuor DESC)

的索引

编辑： OP确认PK为(poclcdde, poclnpol, poclcdce, poclnuor)

我不确定这是否更好，但知道PK确实意味着这是另一种选择......

SELECT
  poclcdde,
  poclnpol,
  poclcdce,
  MAX(poclcdcl)
    KEEP (RANK FIRST
          ORDER BY poclfecb DESC NULLS FIRST,
                   poclnuor DESC
    ) 
      AS poclcdcl,
  MAX(poclnuor)
    KEEP (RANK FIRST
          ORDER BY poclfecb DESC NULLS FIRST,
                   poclnuor DESC
    ) 
      AS poclnuor
FROM
  dtpocl
WHERE
      poclcdre = '02'
  AND poclxope IN ('01', '02')
GROUP BY
  poclcdde,
  poclnpol,
  poclcdce

或者...

SELECT
  sorted.*
FROM
(
  SELECT
    ROW_NUMBER()
      OVER (PARTITION BY poclcdde, poclnpol, poclcdce
                ORDER BY poclfecb DESC NULLS FIRST,
                         poclnuor DESC
      ) 
        AS seqnum
    dtpocl.*
  FROM
    dtpocl
  WHERE
        poclcdre = '02'
    AND poclxope IN ('01', '02')
) 
  sorted
WHERE
  seqnum = 1

Answer 2

这个怎么样？

-- PK is poclcdde, poclnpol, poclcdce & poclnuor

SELECT a.poclcdde,
       a.poclnpol,
       a.poclcdce,
       a.poclcdcl,
       a.poclnuor,
       a.poclfecb
  FROM dtpocl a
 WHERE a.poclcdre = '02'
   AND a.poclxope IN ('01', '02')
   AND a.poclnuor =
      (SELECT MAX (b.poclnuor)
         FROM dtpocl b
        WHERE b.poclcdde = a.poclcdde 
          AND b.poclnpol = a.poclnpol
          AND b.poclcdce = a.poclcdce
          AND b.poclnuor = a.poclnuor
          AND b.poclcdre = a.poclcdre
          AND b.poclxope = a.poclxope)
   AND NVL (a.poclfecb, 99999999) = -- Here you can only use a.poclfecb and not b.poclfecb
      (SELECT MAX (NVL (c.poclfecb, 99999999))
         FROM dtpocl c
        WHERE c.poclcdde = a.poclcdde 
          AND c.poclnpol = a.poclnpol
          AND c.poclcdce = a.poclcdce
          AND c.poclnuor = a.poclnuor
          AND c.poclcdre = a.poclcdre
          AND c.poclxope = a.poclxope)

SQL查询重建问题

2 个答案: