Oracle中游标(Cursor)介绍和使用
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;
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。
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 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(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;
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
附:使用游标
15-1:使用标量变量接收游标数据 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||',岗位:'||v_job||',工资:'||v_sal); END LOOP; CLOSE emp_cursor; END; /
15-2:使用pl/sql纪录变量接收游标数据 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|| ',工资:'||emp_record.sal); END LOOP; CLOSE emp_cursor; END; /
15-3:使用pl/sql集合变量接收游标数据 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|| ',工资:'||emp_table(i).sal); END LOOP; CLOSE emp_cursor; END; /
15-4:在游标for循环中引用已定义游标 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:在游标for循环中直接引用子查询 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; /
15-6:参数游标 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 ||',岗位:'||emp_record.job); END LOOP; END; /
15-7:更新游标行 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 ||',原工资:'||emp_record.sal); UPDATE emp SET sal=sal*1.1 WHERE CURRENT OF emp_cursor; END IF; END LOOP; END; /
15-8:删除游标行 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锁. 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:使用无返回类型的游标变量 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:使用有返回类型的游标变量 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|| ',工资:'||emp_record.sal); END LOOP; CLOSE emp_cursor; END; /
15-12:使用fetch...bulk collect提取所有数据 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 ||',工资:'||emp_table(i).sal); END LOOP; END; /
15-13:使用limit子句限制提取行数 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 ||',工资:'||emp_array(i).sal); END LOOP; EXIT WHEN emp_cursor%NOTFOUND; END LOOP; CLOSE emp_cursor; END; /
15-14:使用cursor表达式 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('部门名:'||v_dname); LOOP FETCH emp_cursor INTO emp_record; EXIT WHEN emp_cursor%NOTFOUND; dbms_output.put_line('----雇员名:'||emp_record.ename ||',岗位:'||emp_record.job); END LOOP; END LOOP; CLOSE dept_cursor; END;