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HomeDatabaseMysql TutorialOracle--plsql游标创建和使用

游标(cursor)是Oracle系统在内存中开辟的一个工作区,在其中存放SELECT语句返回的查询结果。,PL/SQL隐式建立并自动管理这一游

为什么要Oracle游标:

先看这个:

  • DECLARE   
  •  v_empno emp.empno%type;   
  •  v_ename emp.ename%type;   
  • BEGIN   
  •  SELECT empno,ename   
  •  into v_ename,v_empno   
  •  FROM   emp;   
  •  dbms_output.put_line(v_empno||' '||v_ename);  
  • END;  
  • 这个SELECT语句可能返回多条记录,所以这个赋值语句可能是错误的。所以游标可以发挥作用了。

    什么是游标?

    游标(cursor)是Oracle系统在内存中开辟的一个工作区,在其中存放SELECT语句返回的查询结果。

    游标的分类:

    隐式游标:PL/SQL隐式建立并自动管理这一游标。隐式游标也叫做SQL游标。 对于SQL游标,不能对其显式地执行OPEN、CLOSE和FETCH语句,,但是可以使用游标属性从最近执行的SQL语句中获取信息。

    显式游标:由程序员显式说明及控制,用于从表中取出多行数据,并将多行数据一行一行单独处理。

    隐式游标:

  • 由Oracle在内部声明
  • 由Oracle自行管理游标
  • 可以使用游标属性从最近执行的SQL语句中获取信息
  • 用于处理DML语句以及返回单行的查询
  • 隐式游标属性:

    隐式游标举例:

  • VARIABLE rows_deleted VARCHAR2(30)  
  • DECLARE  
  •   v_deptno  NUMBER := 20;  
  • BEGIN    
  •   DELETE FROM  emp  
  •   WHERE  deptno = v_deptno;  
  •   :rows_deleted := (SQL%ROWCOUNT ||' rows deleted.');  
  • END;  
  • /  
  • 返回所删除行的数量

    显式游标:由用户显式声明,查询返回多行记录

  • 使用游标时,select语句查询的结果可以是单条记录,多条记录,也可以是零条记录。
  • 游标工作区中,存在着一个指针(POINTER),在初始状态它指向查询结果的首记录。
  • 要访问查询结果的所有记录,可以通过FETCH语句,进行指针的移动来实现。
  • 使用游标进行操作,包括定义游标、打开游标、提取数据以及关闭游标几步。
  • 更多Oracle相关信息见Oracle 专题页面 ?tid=12

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