Oracle中Cursor介紹和使用

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一  概念 
游標是SQL的一個內存工作區，由系統或用戶以變量的形式定義。游標的作用就是用於臨時存儲從數據庫中提取的數據塊。在某些情況下，需要把數據從存放在磁盤的表中調到計算機內存中進行處理，最后將處理結果顯示出來或最終寫回數據庫。這樣數據處理的速度才會提高，否則頻繁的磁盤數據交換會降低效率。 
二  類型 
  Cursor類型包含三種: 隱式Cursor，顯式Cursor和Ref Cursor（動態Cursor）。 
1． 隱式Cursor: 
1).對於Select …INTO…語句，一次只能從數據庫中獲取到一條數據，對於這種類型的DML Sql語句，就是隱式Cursor。例如：Select /Update / Insert/Delete操作。 
2)作用：可以通過隱式Cusor的屬性來了解操作的狀態和結果，從而達到流程的控制。Cursor的屬性包含： 
SQL%ROWCOUNT 整型 代表DML語句成功執行的數據行數 
SQL%FOUND  布爾型  值為TRUE代表插入、刪除、更新或單行查詢操作成功 
SQL%NOTFOUND 布爾型 與SQL%FOUND屬性返回值相反 
SQL%ISOPEN 布爾型 DML執行過程中為真，結束后為假 
3) 隱式Cursor是系統自動打開和關閉Cursor. 
下面是一個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;

 /

 

2． 顯式Cursor： 
（1） 對於從數據庫中提取多行數據，就需要使用顯式Cursor。顯式Cursor的屬性包含： 
游標的屬性   返回值類型   意    義  
%ROWCOUNT   整型  獲得FETCH語句返回的數據行數  
%FOUND  布爾型 最近的FETCH語句返回一行數據則為真，否則為假  
%NOTFOUND   布爾型 與%FOUND屬性返回值相反  
%ISOPEN 布爾型 游標已經打開時值為真，否則為假  

（2） 對於顯式游標的運用分為四個步驟： 
 定義游標---Cursor  [Cursor Name]  IS; 
 打開游標---Open  [Cursor Name]; 
 操作數據---Fetch  [Cursor name] 
 關閉游標---Close [Cursor Name],這個Step絕對不可以遺漏。 
（3）以下是三種常見顯式Cursor用法。

 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;---定義游標變量
 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
     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;
 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;

 /

 

3． Ref Cursor（動態游標）： 
1） 與隱式Cursor,顯式Cursor的區別：Ref Cursor是可以通過在運行期間傳遞參數來獲取數據結果集。而另外兩種Cursor，是靜態的，在編譯期間就決定數據結果集。 
2） Ref cursor的使用: 
 Type [Cursor type name] is ref cursor 
 Define 動態的Sql語句 
 Open cursor 
 操作數據---Fetch  [Cursor name] 
 Close Cursor 
下面是一個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 動態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.常見Exception 

 1.  錯 誤 名 稱 錯誤代碼    錯 誤 含 義
 2.  CURSOR_ALREADY_OPEN ORA_06511   試圖打開已經打開的游標
 3.  INVALID_CURSOR  ORA_01001   試圖使用沒有打開的游標
 4.  DUP_VAL_ON_INDEX    ORA_00001   保存重復值到惟一索引約束的列中
 5.  ZERO_DIVIDE ORA_01476   發生除數為零的除法錯誤
 6.  INVALID_NUMBER  ORA_01722   試圖對無效字符進行數值轉換
 7.  ROWTYPE_MISMATCH    ORA_06504   主變量和游標的類型不兼容
 8.  VALUE_ERROR ORA_06502   轉換、截斷或算術運算發生錯誤
 9.  TOO_MANY_ROWS   ORA_01422   SELECT…INTO…語句返回多於一行的數據
 10. NO_DATA_FOUND   ORA_01403   SELECT…INTO…語句沒有數據返回
 11. TIMEOUT_ON_RESOURCE ORA_00051   等待資源時發生超時錯誤
 12. TRANSACTION_BACKED_OUT  ORA_00060   由於死鎖，提交失敗
 13. STORAGE_ERROR   ORA_06500   發生內存錯誤
 14. PROGRAM_ERROR   ORA_06501   發生PL/SQL內部錯誤
 15. NOT_LOGGED_ON   ORA_01012   試圖操作未連接的數據庫
 16. LOGIN_DENIED    ORA_01017   在連接時提供了無效用戶名或口令

 

附：使用游標

 15-1:使用標量變量接收游標數據
     DECLARE
       CURSOR emp_cursor IS
         SELECT ename,job,sal FROM emp WHERE deptno=&dno;
       v_ename emp.ename%TYPE;
       v_sal emp.sal%TYPE;
       v_job emp.job%TYPE;
     BEGIN
       OPEN emp_cursor;
       LOOP
         FETCH emp_cursor INTO v_ename,v_job,v_sal;
         EXIT WHEN emp_cursor%NOTFOUND;
         dbms_output.put_line('姓名：'||v_ename||'，崗位：'||v_job||'，工資：'||v_sal);
       END LOOP;
       CLOSE emp_cursor;
     END;
     /
 15-2:使用pl/sql紀錄變量接收游標數據
     DECLARE
       CURSOR emp_cursor IS
         SELECT ename,sal FROM emp ORDER BY sal DESC;
       emp_record emp_cursor%ROWTYPE;
     BEGIN
       OPEN emp_cursor;
       LOOP
         FETCH emp_cursor INTO emp_record;
         EXIT WHEN emp_cursor%NOTFOUND OR emp_cursor%ROWCOUNT>&n;
         dbms_output.put_line('姓名：'||emp_record.ename||
          '，工資：'||emp_record.sal);
       END LOOP;
       CLOSE emp_cursor;
     END;
     /
 15-3:使用pl/sql集合變量接收游標數據
     DECLARE
       CURSOR emp_cursor IS SELECT ename,sal FROM emp
         WHERE lower(job)=lower('&job');
       TYPE emp_table_type IS TABLE OF emp_cursor%ROWTYPE
         INDEX BY BINARY_INTEGER;
       emp_table emp_table_type;
       i INT;
     BEGIN
       OPEN emp_cursor;
       LOOP
         i:=emp_cursor%ROWCOUNT+1;
         FETCH emp_cursor INTO emp_table(i);
         EXIT WHEN emp_cursor%NOTFOUND;
         dbms_output.put_line('姓名：'||emp_table(i).ename||
           '，工資：'||emp_table(i).sal);
       END LOOP;
       CLOSE emp_cursor;
     END;
     /
 15-4:在游標for循環中引用已定義游標
     DECLARE
       CURSOR emp_cursor IS SELECT ename,hiredate FROM emp
         ORDER BY hiredate DESC;
     BEGIN
       FOR emp_record IN emp_cursor LOOP
         dbms_output.put_line('姓名：'||emp_record.ename
           ||',工作日期：'||emp_record.hiredate);
         EXIT WHEN emp_cursor%ROWCOUNT=&n;
       END LOOP;
     END;
     /
 15-5:在游標for循環中直接引用子查詢
     BEGIN
       FOR emp_record IN (SELECT ename,hiredate,rownum FROM emp
         ORDER BY hiredate) LOOP
         dbms_output.put_line('姓名：'||emp_record.ename
          ||',工作日期：'||emp_record.hiredate);
         EXIT WHEN emp_record.rownum=&n;
       END LOOP;
     END;
     /
 15-6:參數游標
     DECLARE
       CURSOR emp_cursor(dno NUMBER) IS
         SELECT ename,job FROM emp WHERE deptno=dno;
     BEGIN
       FOR emp_record IN emp_cursor(&dno) LOOP
         dbms_output.put_line('姓名：'||emp_record.ename
           ||',崗位：'||emp_record.job);
       END LOOP;
     END;
     /
 15-7:更新游標行
     DECLARE
       CURSOR emp_cursor IS
         SELECT ename,sal,deptno FROM emp FOR UPDATE;
       dno INT:=&no;
     BEGIN
       FOR emp_record IN emp_cursor LOOP
         IF emp_record.deptno=dno THEN
            dbms_output.put_line('姓名:'||emp_record.ename
             ||',原工資:'||emp_record.sal);
            UPDATE emp SET sal=sal*1.1 WHERE CURRENT OF emp_cursor;
         END IF;
       END LOOP;
     END;
     /
 15-8:刪除游標行
     DECLARE
       CURSOR emp_cursor IS
         SELECT ename FROM emp FOR UPDATE;
       name VARCHAR2(10):=lower('&name');
     BEGIN
       FOR emp_record IN emp_cursor LOOP
         IF lower(emp_record.ename)=name THEN
            DELETE FROM emp WHERE CURRENT OF emp_cursor;
         ELSE
            dbms_output.put_line('姓名:'||emp_record.ename);
         END IF;
       END LOOP;
     END;
     /
 15-9:使用of子句在特定表上加行共享鎖．
     DECLARE
       CURSOR emp_cursor IS
         SELECT a.dname,b.ename FROM dept a JOIN emp b
         ON a.deptno=b.deptno
         FOR UPDATE OF b.deptno;
       name VARCHAR2(10):=LOWER('&name');
     BEGIN
       FOR emp_record IN emp_cursor LOOP
         IF LOWER(emp_record.dname)=name THEN
           dbms_output.put_line('姓名:'||emp_record.ename);
           DELETE FROM emp WHERE CURRENT OF emp_cursor;
         END IF;
       END LOOP;
     END;
     /
 15-10:使用無返回類型的游標變量
     DECLARE
       TYPE ref_cursor_type IS REF CURSOR;
       ref_cursor ref_cursor_type;
       v1 NUMBER(6);
       v2 VARCHAR2(10);
     BEGIN
       OPEN ref_cursor FOR
         SELECT &col1 col1,&col2 col2 FROM &table WHERE &cond;
       LOOP
         FETCH ref_cursor INTO v1,v2;
         EXIT WHEN ref_cursor%NOTFOUND;
         dbms_output.put_line('col1='||v1||',col2='||v2);
       END LOOP;
       CLOSE ref_cursor;
     END;
     /
 15-11:使用有返回類型的游標變量
     DECLARE
       TYPE emp_cursor_type IS REF CURSOR RETURN emp%ROWTYPE;
       emp_cursor emp_cursor_type;
       emp_record emp%ROWTYPE;
     BEGIN
       OPEN emp_cursor FOR SELECT * FROM emp
         WHERE deptno=&dno;
       LOOP
         FETCH emp_cursor INTO emp_record;
         EXIT WHEN emp_cursor%NOTFOUND;
         dbms_output.put_line('姓名:'||emp_record.ename||
           ',工資:'||emp_record.sal);
       END LOOP;
       CLOSE emp_cursor;
     END;
     /
 15-12:使用fetch...bulk collect提取所有數據
     DECLARE
       CURSOR emp_cursor IS
         SELECT * FROM emp WHERE LOWER(job)=LOWER('&job');
       TYPE emp_table_type IS TABLE OF emp%ROWTYPE;
       emp_table emp_table_type;
     BEGIN
       OPEN emp_cursor;
       FETCH emp_cursor BULK COLLECT INTO emp_table;
       CLOSE emp_cursor;
       FOR i IN 1.. emp_table.COUNT LOOP
         dbms_output.put_line('姓名:'||emp_table(i).ename
           ||',工資:'||emp_table(i).sal);
       END LOOP;
     END;
     /
 15-13:使用limit子句限制提取行數
     DECLARE
       CURSOR emp_cursor IS SELECT * FROM emp;
       TYPE emp_array_type IS VARRAY(5) OF emp%ROWTYPE;
       emp_array emp_array_type;
     BEGIN
       OPEN emp_cursor;
       LOOP
         FETCH emp_cursor BULK COLLECT INTO emp_array LIMIT &rows;
         FOR i IN 1..emp_array.COUNT LOOP
           dbms_output.put_line('姓名:'||emp_array(i).ename
             ||',工資:'||emp_array(i).sal);
         END LOOP;
         EXIT WHEN emp_cursor%NOTFOUND;
       END LOOP;
       CLOSE emp_cursor;
     END;
     /
 15-14:使用cursor表達式
     DECLARE
       CURSOR dept_cursor(no NUMBER) IS
          SELECT a.dname,CURSOR(SELECT * FROM emp
          WHERE deptno=a.deptno)
          FROM dept a WHERE a.deptno=no;
       TYPE ref_cursor_type IS REF CURSOR;
       emp_cursor ref_cursor_type;
       emp_record emp%ROWTYPE;
       v_dname dept.dname%TYPE;
     BEGIN
       OPEN dept_cursor(&dno);
       LOOP
          FETCH dept_cursor INTO v_dname,emp_cursor;
          EXIT WHEN dept_cursor%NOTFOUND;
          dbms_output.put_line('部門名:'||v_dname);
          LOOP
            FETCH emp_cursor INTO emp_record;
            EXIT WHEN emp_cursor%NOTFOUND;
            dbms_output.put_line('----雇員名:'||emp_record.ename
             ||',崗位:'||emp_record.job);
          END LOOP;
       END LOOP;
       CLOSE dept_cursor;
     END;
     /