Oracle中Cursor介绍

一  概念
游标是SQL的一个内存工作区，由系统或用户以变量的形式定义。游标的作用就是用于临时存储从数据库中提取的数据块。在某些情况下，需要把数据从存放在磁盘的表中调到计算机内存中进行处理，最后将处理结果显示出来或最终写回数据库。这样数据处理的速度才会提高，否则频繁的磁盘数据交换会降低效率。
二  类型
  Cursor类型包含三种: 隐式Cursor，显式Cursor和Ref Cursor（动态Cursor）。
1． 隐式Cursor:
1).对于Select …INTO…语句，一次只能从数据库中获取到一条数据，对于这种类型的DML Sql语句，就是隐式Cursor。例如：Select /Update / Insert/Delete操作。
2)作用：可以通过隐式Cusor的属性来了解操作的状态和结果，从而达到流程的控制。Cursor的属性包含：
SQL%ROWCOUNT 整型 代表DML语句成功执行的数据行数
SQL%FOUND  布尔型  值为TRUE代表插入、删除、更新或单行查询操作成功
SQL%NOTFOUND 布尔型 与SQL%FOUND属性返回值相反
SQL%ISOPEN 布尔型 DML执行过程中为真，结束后为假
3) 隐式Cursor是系统自动打开和关闭Cursor.
下面是一个Sample：

 
Set Serveroutput on;   
  
begin  
    update t_contract_master set liability_state = 1 where policy_code = '123456789';   
       
    if SQL%Found then  
       dbms_output.put_line('the Policy is updated successfully.');   
       commit;   
    else  
      dbms_output.put_line('the policy is updated failed.');   
    end if;   
  
end;   
  
/  

Set Serveroutput on;

begin
    update t_contract_master set liability_state = 1 where policy_code = '123456789';
    
    if SQL%Found then
       dbms_output.put_line('the Policy is updated successfully.');
       commit;
    else
      dbms_output.put_line('the policy is updated failed.');
    end if;

end;

/

在PL/SQL中run:

SQL>    
    
the policy is updated failed.   
    
PL/SQL procedure successfully completed  

SQL> 
 
the policy is updated failed.
 
PL/SQL procedure successfully completed

2． 显式Cursor：
（1） 对于从数据库中提取多行数据，就需要使用显式Cursor。显式Cursor的属性包含：
游标的属性   返回值类型   意    义 
%ROWCOUNT   整型  获得FETCH语句返回的数据行数 
%FOUND  布尔型 最近的FETCH语句返回一行数据则为真，否则为假 
%NOTFOUND   布尔型 与%FOUND属性返回值相反 
%ISOPEN 布尔型 游标已经打开时值为真，否则为假 

（2） 对于显式游标的运用分为四个步骤：
 定义游标---Cursor  [Cursor Name]  IS;
 打开游标---Open  [Cursor Name];
 操作数据---Fetch  [Cursor name]
 关闭游标---Close [Cursor Name],这个Step绝对不可以遗漏。
（3）以下是三种常见显式Cursor用法。
1）

Set serveroutput on;   
  
declare    
    ---define Cursor   
    Cursor cur_policy is  
     select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account   
     from t_contract_master cm   
     where cm.liability_state = 2   
     and cm.policy_type = 1   
     and cm.policy_cate in ('2','3','4')   
     and rownum < 5   
     order by cm.policy_code desc;   
    curPolicyInfo cur_policy%rowtype;---定义游标变量   
Begin  
   open cur_policy; ---open cursor   
   Loop    
     --deal with extraction data from DB   
     Fetch cur_policy into curPolicyInfo;   
     Exit when cur_policy%notfound;   
            
     Dbms_Output.put_line(curPolicyInfo.policy_code);   
   end loop;   
   Exception    
     when others then  
         close cur_policy;   
         Dbms_Output.put_line(Sqlerrm);   
            
   if cur_policy%isopen then     
    --close cursor    
      close cur_policy;   
   end if;   
end;   
  
/  

Set serveroutput on;

declare 
    ---define Cursor
    Cursor cur_policy is
     select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account
     from t_contract_master cm
     where cm.liability_state = 2
     and cm.policy_type = 1
     and cm.policy_cate in ('2','3','4')
     and rownum < 5
     order by cm.policy_code desc;
    curPolicyInfo cur_policy%rowtype;---定义游标变量
Begin
   open cur_policy; ---open cursor
   Loop 
     --deal with extraction data from DB
     Fetch cur_policy into curPolicyInfo;
     Exit when cur_policy%notfound;
         
     Dbms_Output.put_line(curPolicyInfo.policy_code);
   end loop;
   Exception 
     when others then
         close cur_policy;
         Dbms_Output.put_line(Sqlerrm);
         
   if cur_policy%isopen then  
	--close cursor 
      close cur_policy;
   end if;
end;

/

2）

Set serveroutput on;   
  
declare    
    Cursor cur_policy is  
     select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account   
     from t_contract_master cm   
     where cm.liability_state = 2   
     and cm.policy_type = 1   
     and cm.policy_cate in ('2','3','4')   
     and rownum < 5   
     order by cm.policy_code desc;   
     v_policyCode t_contract_master.policy_code%type;   
     v_applicantId t_contract_master.applicant_id%type;   
     v_periodPrem t_contract_master.period_prem%type;   
     v_bankCode t_contract_master.bank_code%type;   
     v_bankAccount t_contract_master.bank_account%type;   
Begin  
   open cur_policy;   
   Loop    
     Fetch cur_policy into v_policyCode,   
                           v_applicantId,   
                           v_periodPrem,   
                           v_bankCode,   
                           v_bankAccount;   
     Exit when cur_policy%notfound;   
            
     Dbms_Output.put_line(v_policyCode);   
   end loop;   
   Exception    
     when others then  
         close cur_policy;   
         Dbms_Output.put_line(Sqlerrm);   
            
   if cur_policy%isopen then      
      close cur_policy;   
   end if;   
end;   
/  

Set serveroutput on;

declare 
    Cursor cur_policy is
     select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account
     from t_contract_master cm
     where cm.liability_state = 2
     and cm.policy_type = 1
     and cm.policy_cate in ('2','3','4')
     and rownum < 5
     order by cm.policy_code desc;
     v_policyCode t_contract_master.policy_code%type;
     v_applicantId t_contract_master.applicant_id%type;
     v_periodPrem t_contract_master.period_prem%type;
     v_bankCode t_contract_master.bank_code%type;
     v_bankAccount t_contract_master.bank_account%type;
Begin
   open cur_policy;
   Loop 
     Fetch cur_policy into v_policyCode,
                           v_applicantId,
                           v_periodPrem,
                           v_bankCode,
                           v_bankAccount;
     Exit when cur_policy%notfound;
         
     Dbms_Output.put_line(v_policyCode);
   end loop;
   Exception 
     when others then
         close cur_policy;
         Dbms_Output.put_line(Sqlerrm);
         
   if cur_policy%isopen then   
      close cur_policy;
   end if;
end;
/

3）Sql代码

Set serveroutput on;   
  
declare    
    Cursor cur_policy is  
     select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account   
     from t_contract_master cm   
     where cm.liability_state = 2   
     and cm.policy_type = 1   
     and cm.policy_cate in ('2','3','4')   
     and rownum < 5   
     order by cm.policy_code desc;   
Begin  
   For rec_Policy in cur_policy loop   
       Dbms_Output.put_line(rec_policy.policy_code);   
   end loop;   
   Exception    
     when others then  
         Dbms_Output.put_line(Sqlerrm);   
            
end;   
  
/  

Set serveroutput on;

declare 
    Cursor cur_policy is
     select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account
     from t_contract_master cm
     where cm.liability_state = 2
     and cm.policy_type = 1
     and cm.policy_cate in ('2','3','4')
     and rownum < 5
     order by cm.policy_code desc;
Begin
   For rec_Policy in cur_policy loop
       Dbms_Output.put_line(rec_policy.policy_code);
   end loop;
   Exception 
     when others then
         Dbms_Output.put_line(Sqlerrm);
         
end;

/

run pl/sql,执行结果如下：

SQL>    
    
8780203932   
8780203227   
8780203218   
8771289268   
    
PL/SQL procedure successfully completed  

SQL> 
 
8780203932
8780203227
8780203218
8771289268
 
PL/SQL procedure successfully completed

3． Ref Cursor（动态游标）：
1） 与隐式Cursor,显式Cursor的区别：Ref Cursor是可以通过在运行期间传递参数来获取数据结果集。而另外两种Cursor，是静态的，在编译期间就决定数据结果集。
2） Ref cursor的使用:
 Type [Cursor type name] is ref cursor
 Define 动态的Sql语句
 Open cursor
 操作数据---Fetch  [Cursor name]
 Close Cursor
下面是一个Sample：

Set serveroutput on;   
  
Declare  
    ---define cursor type name   
    type cur_type is ref cursor;   
    cur_policy cur_type;   
    sqlStr varchar2(500);   
    rec_policy t_contract_master%rowtype;   
begin  
   ---define 动态Sql   
   sqlStr := 'select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account from t_contract_master cm   
     where cm.liability_state = 2    
     and cm.policy_type = 1    
     and cm.policy_cate in (2,3,4)    
     and rownum < 5    
     order by cm.policy_code desc ';   
---Open Cursor   
  open cur_policy for sqlStr;   
  loop   
       fetch cur_policy into rec_policy.policy_code, rec_policy.applicant_id, rec_policy.period_prem,rec_policy.bank_code,rec_policy.bank_account;   
       exit when cur_policy%notfound;   
          
       Dbms_Output.put_line('Policy_code:'||rec_policy.policy_code);   
     
  end loop;   
close cur_policy;       
  
end;   
/  

Set serveroutput on;

Declare
    ---define cursor type name
    type cur_type is ref cursor;
    cur_policy cur_type;
    sqlStr varchar2(500);
    rec_policy t_contract_master%rowtype;
begin
   ---define 动态Sql
   sqlStr := 'select cm.policy_code, cm.applicant_id, cm.period_prem,cm.bank_code,cm.bank_account from t_contract_master cm
     where cm.liability_state = 2 
     and cm.policy_type = 1 
     and cm.policy_cate in (2,3,4) 
     and rownum < 5 
     order by cm.policy_code desc ';
---Open Cursor
  open cur_policy for sqlStr;
  loop
       fetch cur_policy into rec_policy.policy_code, rec_policy.applicant_id, rec_policy.period_prem,rec_policy.bank_code,rec_policy.bank_account;
       exit when cur_policy%notfound;
       
       Dbms_Output.put_line('Policy_code:'||rec_policy.policy_code);
  
  end loop;
close cur_policy;    

end;
/

4.常见Exception

 
1.  错 误 名 称 错误代码    错 误 含 义      
2.  CURSOR_ALREADY_OPEN ORA_06511   试图打开已经打开的游标      
3.  INVALID_CURSOR  ORA_01001   试图使用没有打开的游标      
4.  DUP_VAL_ON_INDEX    ORA_00001   保存重复值到惟一索引约束的列中      
5.  ZERO_DIVIDE ORA_01476   发生除数为零的除法错误      
6.  INVALID_NUMBER  ORA_01722   试图对无效字符进行数值转换      
7.  ROWTYPE_MISMATCH    ORA_06504   主变量和游标的类型不兼容      
8.  VALUE_ERROR ORA_06502   转换、截断或算术运算发生错误      
9.  TOO_MANY_ROWS   ORA_01422   SELECT…INTO…语句返回多于一行的数据      
10. NO_DATA_FOUND   ORA_01403   SELECT…INTO…语句没有数据返回      
11. TIMEOUT_ON_RESOURCE ORA_00051   等待资源时发生超时错误      
12. TRANSACTION_BACKED_OUT  ORA_00060   由于死锁，提交失败      
13. STORAGE_ERROR   ORA_06500   发生内存错误      
14. PROGRAM_ERROR   ORA_06501   发生PL/SQL内部错误      
15. NOT_LOGGED_ON   ORA_01012   试图操作未连接的数据库      
16. LOGIN_DENIED    ORA_01017   在连接时提供了无效用户名或口令