如何从执行动态 SQL 的 Oracle PL/SQL 匿名块返回结果集/游标?

How to return a resultset / cursor from a Oracle PL/SQL anonymous block that executes Dynamic SQL?(如何从执行动态 SQL 的 Oracle PL/SQL 匿名块返回结果集/游标?)

问题描述

我有这张桌子:

ALLITEMS
---------------
ItemId  | Areas
---------------
1       | EAST
2       | EAST
3       | SOUTH
4       | WEST

DDL:

drop table allitems;

Create Table Allitems(ItemId Int,areas Varchar2(20));
Insert Into Allitems(Itemid,Areas) Values(1,'east');
Insert Into Allitems(ItemId,areas) Values(2,'east');
insert into allitems(ItemId,areas) values(3,'south');
insert into allitems(ItemId,areas) values(4,'east');

在 MSSQL 中，我可以从动态 SQL 中获取游标:

In MSSQL, to get a cursor from a dynamic SQL I can do:

DECLARE @v_sqlStatement VARCHAR(2000);
SET @v_Sqlstatement = 'SELECT * FROM ALLITEMS';
EXEC (@v_sqlStatement); --returns a resultset/cursor, just like calling SELECT 

在 Oracle 中，我需要使用 PL/SQL 块:

In Oracle, I need to use a PL/SQL Block:

SET AUTOPRINT ON;
DECLARE
 V_Sqlstatement Varchar2(2000);
 outputData SYS_REFCURSOR;
BEGIN
 V_Sqlstatement := 'SELECT * FROM ALLITEMS';
 OPEN outputData for v_Sqlstatement; 
End;
--result is : anonymous block completed

**但我得到的只是

匿名区块已完成".

如何让它返回光标?

(我知道如果我做 AUTOPRINT，它会打印出 REFCURSOR 中的信息(上面的代码中没有打印，但那是另一个问题))

我将从代码(ODBC、C++)中调用这个动态 SQL，我需要它来返回一个游标.怎么样?

I will be calling this Dynamic SQL from code (ODBC,C++), and I need it to return a cursor. How?

推荐答案

您可以编写一个 PL/SQL 函数来返回该游标(或者，如果您有更多与此相关的代码，您可以将该函数放入一个包中):

You can write a PL/SQL function to return that cursor (or you could put that function in a package if you have more code related to this):

CREATE OR REPLACE FUNCTION get_allitems
  RETURN SYS_REFCURSOR
AS
  my_cursor SYS_REFCURSOR;
BEGIN
  OPEN my_cursor FOR SELECT * FROM allitems;
  RETURN my_cursor;
END get_allitems;

这将返回光标.

如果可能，请确保不要将 SELECT-String 放入 PL/SQL 中的引号中.把它放在字符串中意味着在编译时无法检查它，并且每次使用时都必须对其进行解析.

Make sure not to put your SELECT-String into quotes in PL/SQL when possible. Putting it in strings means that it can not be checked at compile time, and that it has to be parsed whenever you use it.

如果您确实需要使用动态 SQL，您可以将查询放在单引号中:

If you really need to use dynamic SQL you can put your query in single quotes:

  OPEN my_cursor FOR 'SELECT * FROM allitems';

每当调用函数时都必须解析此字符串，这通常会变慢并在运行时隐藏查询中的错误.

This string has to be parsed whenever the function is called, which will usually be slower and hides errors in your query until runtime.

确保尽可能使用绑定变量以避免硬解析:

Make sure to use bind-variables where possible to avoid hard parses:

  OPEN my_cursor FOR 'SELECT * FROM allitems WHERE id = :id' USING my_id;

这篇关于如何从执行动态 SQL 的 Oracle PL/SQL 匿名块返回结果集/游标?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！