Question

我有一个非常复杂的视图，其格式如下

create or replace view loan_vw as 
select * from (with loan_info as (select loan_table.*,commission_table.* 
                                   from loan_table,
                                  commission_table where 
                                  contract_id=commission_id)
                select /*complex transformations */ from loan_info
                where type <> 'PRINCIPAL'
                union all 
                select /*complex transformations */ from loan_info
                where type = 'PRINCIPAL')

现在，如果执行以下操作，则查询将挂起

         select * from loan_vw where contract_id='HA001234TY56';

但是，如果我在子查询重构中进行硬编码或在同一会话中使用包级变量，则查询将在一秒钟内返回

create or replace view loan_vw as 
        select * from (with loan_info as (select loan_table.*,commission_table.* 
                                           from loan_table,
                                          commission_table where 
                                          contract_id=commission_id
                                          and contract_id='HA001234TY56'
                                          )
                        select /*complex transformations */ from loan_info
                        where type <> 'PRINCIPAL'
                        union all 
                        select /*complex transformations */ from loan_info
                        where type = 'PRINCIPAL')

由于我使用Business对象，因此无法使用包级变量

所以我的问题是Oracle中有一个提示，告诉优化器首先在子查询重构中检查loan_vw中的contract_id。

根据要求，使用的分析函数如下

select value_date, item, credit_entry, item_paid
from (
  select value_date, item, credit_entry, debit_entry,
    greatest(0, least(credit_entry, nvl(sum(debit_entry) over (), 0)
      - nvl(sum(credit_entry) over (order by value_date
          rows between unbounded preceding and 1 preceding), 0))) as item_paid
  from your_table
)
where item is not null;

在遵循Boneist和MarcinJ的建议之后，我删除了Sub查询重构（CTE），并编写了一个如下所示的长查询，将性能从3分钟提高到了0.156秒。

  create or replace view loan_vw as
  select /*complex transformations */
                               from loan_table,
                              commission_table where 
                              contract_id=commission_id
               and loan_table.type <> 'PRINCIPAL'
  union all
  select /*complex transformations */
                               from loan_table,
                              commission_table where 
                              contract_id=commission_id
               and loan_table.type = 'PRINCIPAL'

Answer 1

这些转换真的需要使用UNION ALL这么复杂吗？优化您看不到的东西确实很困难，但是您是否尝试过摆脱CTE并内联实现计算？

CREATE OR REPLACE VIEW loan_vw AS
SELECT loan.contract_id
     , CASE commission.type -- or wherever this comes from
         WHEN 'PRINCIPAL'
         THEN SUM(whatever) OVER (PARTITION BY loan.contract_id, loan.type) -- total_whatever

         ELSE SUM(something_else) OVER (PARTITION BY loan.contract_id, loan.type) -- total_something_else
      END AS whatever_something
  FROM loan_table loan 
 INNER 
  JOIN commission_table commission
    ON loan.contract_id = commission.commission_id

请注意，如果您的分析函数没有PARTITION BY contract_id，则将根本无法在该contract_id列上使用索引。

Take a look at this db fiddle（您必须在最后一个结果表上单击...才能扩展结果）。在这里，loan表具有一个索引（PK）contract_id列，还有一个some_other_id，它也是唯一的，但没有索引，并且外部查询的谓词仍在{{1 }}。如果比较contract_id和partition by contract的计划，您会发现partition by other id计划中根本没有使用索引：partition by other id中有一个TABLE ACCESS与FULL中的INDEX-UNIQUE SCAN相比，贷款表中的所有选项。这显然是因为优化器无法自行解决partition by contract和contract_id之间的关系，因此它需要在整个窗口上运行some_other_id或SUM而不是整个窗口通过索引使用限制窗口行数。

如果您有包含这些合同的维度表，您还可以尝试将其加入结果，并从维度表（而不是最可能的巨额贷款事实表）中暴露AVG。有时，这可以通过使用维表上的唯一索引来改善基数估计。

同样，在没有查询甚至计划的情况下，优化黑匣子确实非常困难，因此我们不知道发生了什么。例如，可以不必要地实现CTE或子查询。

Answer 2

感谢您进行更新，以包括列列表的示例。

鉴于您的更新查询，我建议您更改视图（或者，如果您的原始视图可用于查询多个contract_id，则可以创建第二个视图来查询单个contract_id-当然，除非原始视图的结果仅适用于单个contract_ids！），例如：

CREATE OR REPLACE VIEW loan_vw AS 
WITH loan_info AS (SELECT l.*, c.* -- for future-proofing, you should list the column names explicitly; if this statement is rerun and there's a column with the same name in both tables, it'll fail.
                   FROM   loan_table l
                          INNER JOIN commission_table c ON l.contract_id = c.commission_id -- you should always alias the join condition columns for ease of maintenance.
                  )
SELECT value_date,
     item,
     credit_entry,
     debit_entry,
     GREATEST(0,
            LEAST(credit_entry,
                NVL(SUM(debit_entry) OVER (PARTITION BY contract_id), 0)
                  - NVL(SUM(credit_entry) OVER (PARTITION BY contract_id ORDER BY value_date ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING), 0))) AS item_paid
FROM   loan_info
WHERE  TYPE <> 'PRINCIPAL'
UNION ALL
SELECT ...
FROM   loan_info
WHERE  TYPE = 'PRINCIPAL';

请注意，我已将您的联接转换为ANSI语法，因为它比旧式联接更容易理解（更容易将联接条件与谓词分开，一开始！）。

在执行任何其他SQL之前先执行子查询重构

2 个答案: