Oracle中Cursor介绍

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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