如何在oracle上选择可选参数（减少oracle的执行时间）？

Question

我必须减少它的执行时间。当我刚刚插入“：i_member_name”时，这个语句处理浪费了大约30分钟，所有其他都是空的。

SELECT 

A.MEMBER_NUM, A.MEMBER_NAME, B.MEMBER_INFO FROM REG_MEMBER A, MEMBER_DETAIL B

WHERE A.MEMBER_ID = B.MEMBER_ID 

AND (LOWER(A.MEMBER_NAME)  LIKE LOWER(:i_member_name || '%'))     

AND (LOWER(B.MEMBER_INFO) LIKE LOWER(:i_member_info || '%'))

AND (A.MEMBER_NUM  LIKE :i_member_num || '%')

AND (LOWER(B.MEMBER_ADD) LIKE LOWER('%' || :i_member_add || '%'))

如果我这样执行，那没关系，只是浪费了 30 秒。

SELECT 

    A.MEMBER_NUM, A.MEMBER_NAME, B.MEMBER_INFO FROM REG_MEMBER A, MEMBER_DETAIL B

    WHERE A.MEMBER_ID = B.MEMBER_ID 

    AND (LOWER(A.MEMBER_NAME)  LIKE LOWER(:i_member_name || '%'))     

  --AND (LOWER(B.MEMBER_INFO) LIKE LOWER(:i_member_info || '%'))

  --AND (A.MEMBER_NUM  LIKE :i_member_num || '%')

  --AND (LOWER(B.MEMBER_ADD) LIKE LOWER('%' || :i_member_add || '%'))

所以我有一个问题：如何检查参数是否为空，然后不要读取更多执行时间。像这样的

         SELECT A.MEMBER_NUM, A.MEMBER_NAME, B.MEMBER_INFO FROM REG_MEMBER A, MEMBER_DETAIL B         
                    WHERE 
(LOWER(A.MEMBER_NAME)  LIKE LOWER(:i_member_name || '%'))    
         and   case when :i_member_num is null then return 
        else (A.MEMBER_NUM LIKE :i_member_num || '%')
    end

Answer 1

在 SQL 中检查可选参数的最快方法通常是使用NVL。

Oracle 通常可以将NVL 表达式扩展为两个单独的子计划。 FILTER 操作将在运行时仅选择计划的一部分。例如，它可以使用带有绑定值的INDEX RANGE SCAN，如'Smith%'，它是sargable；它可以使用TABLE ACCESS FULL 和绑定值，如NULL，这是不可分割的。

以下是使用问题中一小部分对象的示例：

--Create table and index.
create table reg_member(member_num number, member_name varchar2(100));
create index reg_member_idx on reg_member(lower(member_name));

--Generate explain plan.
EXPLAIN PLAN FOR
SELECT
    A.MEMBER_NUM, A.MEMBER_NAME
FROM REG_MEMBER A
WHERE NVL(:i_member_name, LOWER(A.MEMBER_NAME)) = LOWER(A.MEMBER_NAME);

--Show explain plan.
select * from table(dbms_xplan.display);

Plan hash value: 3501926772

----------------------------------------------------------------------------------------------------------
| Id  | Operation                              | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                       |                 |     2 |   130 |     3   (0)| 00:00:01 |
|   1 |  VIEW                                  | VW_ORE_377C5901 |     2 |   130 |     3   (0)| 00:00:01 |
|   2 |   UNION-ALL                            |                 |       |       |            |          |
|*  3 |    FILTER                              |                 |       |       |            |          |
|   4 |     TABLE ACCESS BY INDEX ROWID BATCHED| REG_MEMBER      |     1 |   117 |     1   (0)| 00:00:01 |
|*  5 |      INDEX RANGE SCAN                  | REG_MEMBER_IDX  |     1 |       |     1   (0)| 00:00:01 |
|*  6 |    FILTER                              |                 |       |       |            |          |
|*  7 |     TABLE ACCESS FULL                  | REG_MEMBER      |     1 |   117 |     2   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------------

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

   3 - filter(:I_MEMBER_NAME IS NOT NULL)
   5 - access(LOWER("MEMBER_NAME")=:I_MEMBER_NAME)
   6 - filter(:I_MEMBER_NAME IS NULL)
   7 - filter(LOWER("MEMBER_NAME") IS NOT NULL)

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

NVL FILTER 操作在某些情况下可以很好地工作。但很难说它是否能解决您的具体问题，因为变量太多：对象是否有正确的索引，所有谓词如何协同工作等等。但NVL 是一个很好的起点。