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I'm really new to Oracle PL/SQL, but experienced in Sql Server, and I'm trying to learn the ins and outs of it. For an introductory to it I've decided to optimize a query that is generated as a C# string and then executed as a text SqlCommand. So I'm trying to create a stored proc but to include all the variations of how the where clause can be generated, it's causing it to run ~40 seconds while the C# generated string executes in ~3 seconds. Here's an example of what I mean by the variations of the where clause...

declare  
searchType nvarchar2(3); -- options are 'x', 'y', 'z'  
searchDesc nvarchar2(4); -- options are '1', '2', '3'  
searchValue nvarchar2(5);

begin  

select count(*)  
from tbl_A a
where ((searchType = 'x' 
    and ((a.desc_X = searchDesc and a.value_1 = searchValue)
      or (a.desc_X = searchDesc and a.value_2 = searchValue)
      or (a.desc_X = searchDesc and a.value_3 = searchValue)
    )
  )
  or (searchType = 'y' 
    and ((a.desc_Y = searchDesc and a.value_1 = searchValue)
      or (a.desc_Y = searchDesc and a.value_2 = searchValue)
      or (a.desc_Y = searchDesc and a.value_3 = searchValue)
    )
  )
  or (searchType = 'z' 
    and ((a.desc_Z = searchDesc and a.value_1 = searchValue)
      or (a.desc_Z = searchDesc and a.value_2 = searchValue)
      or (a.desc_Z = searchDesc and a.value_3 = searchValue)
    )
  )
)

end;

So what I'm wondering is, is it possible to have a select statement that can execute dynamic sql in the where clause. Or does the entire statement need to be dynamic sql. Below is an example of what I'm questioning...

declare
whereClause varchar2(500);  
searchType nvarchar2(3); -- options are 'x', 'y', 'z'  
searchDesc nvarchar2(4); -- options are '1', '2', '3'  
searchValue nvarchar2(5);  

begin

select case
    when searchType = 'x' then 'a.desc_X = :desc and a.value_1 = :val'
    when searchType = 'y' then 'a.desc_Y = :desc and a.value_2 = :val'
    when searchType = 'z' then 'a.desc_Z = :desc and a.value_3 = :val'
    end
into whereClause
from dual;

select count(*)
from tbl_A a
where (
    execute immediately whereClause using searchDesc, searchValue
)

end;

When I tried to execute it as all dynamic sql, it still took ~15 seconds to execute. So if anyone has a better way of handling the many where clause variations, I'm open to suggestions.

4

1 回答 1

2

像这样使用太多的 OR 会导致性能下降。如果你总是有一组固定的参数，你可以这样做：

declare

    stmt varchar2(1500);  
    searchType nvarchar2(3); -- options are 'x', 'y', 'z'  
    searchDesc nvarchar2(4); -- options are '1', '2', '3'  
    searchValue nvarchar2(5);  

    n pls_integer;

begin

    stmt := 'select count(*) from tbl_A a where (';

     case
        when searchType = 'x' then stmt := stmt || 'a.desc_X = :desc and a.value_1 = :val';
        when searchType = 'y' then stmt := stmt || 'a.desc_Y = :desc and a.value_2 = :val';
        when searchType = 'z' then stmt := stmt || 'a.desc_Z = :desc and a.value_3 = :val';
    end case;

    stmt := stmt ||')';


    execute immediately stmt using searchDesc, searchValue
    into n;

end;

请注意 - 与 T-SQL 不同 - 在 PL/SQL 中，我们需要将结果集选择为变量。我提出了一个整数，因为您的示例代码只是 SELECT COUNT(*)。您的真实查询将需要与查询投影匹配的变量，可能是记录类型或集合。

于 2013-06-18T16:02:35.150 回答