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oracle数据库中关于游标的常见用法

时间:2021-07-01 10:21:17 帮助过:18人阅读

1、什么是游标 游标是一种PL/SQL控制结构,可以对SQL语句进行显示控制,便于对表的数据逐条进行处理 2、游标分类 显示游标: Declared and named by the programmer 隐式游标: Declared for all DML and PL/SQL SELECT statements 3、游标的属性: %FOUND:Ev

1、什么是游标

游标是一种PL/SQL控制结构,可以对SQL语句进行显示控制,便于对表的数据逐条进行处理

2、游标分类

显示游标: Declared and named by the programmer

隐式游标: Declared for all DML and PL/SQL SELECT statements



3、游标的属性:

%FOUND:Evaluates to TRUE if the most recent SQL statement affects one or more rows

%NOTFOUND:和%FOUND相反

%ISOPEN:是一个布尔值,如果游标打开,则为TRUE, 如果游标关闭,则为FALSE.对于隐式游标而言SQL%ISOPEN总是FALSE,这是因为隐式游标在DML语句执行时打开,结束时就立即关闭。

%ROWCOUNT:Number of records affected by the most recent SQL statement



注意:dbms_output.put_line();这个是不能打印boolean型的,解决方法

if b then

dbms_output.put_line('b=true');

end if;



或者:

declare

b boolean;

begin

b := true;

dbms_output.put_line((case when b then 'true' else 'false' end));

end;



对于null,课先使用NVL()或者decode()处理



显示游标:需要手动open和close

例如:

DECLARE

CURSOR mycursor IS

SELECT * FROM dept;

myrecord dept%ROWTYPE;

BEGIN

OPEN mycursor;

FETCH mycursor INTO myrecord;

WHILE mycursor%FOUND LOOP

DBMS_OUTPUT.PUT_LINE(myrecord.deptno||' '||myrecord.dname||' '||myrecord.loc);

FETCH mycursor INTO myrecord;

END LOOP;

CLOSE mycursor;

END;

注意:在进行while循环前,必须先有一个FETCH..INTO操作,否者%FOUND总是返 回false



带参数的游标:

DECLARE

CURSOR mycursor(num varchar2) IS

SELECT * FROM DEPT WHERE deptno=num;

myrecord dept%ROWTYPE;

BEGIN

OPEN mycursor(10);

LOOP

FETCH mycursor INTO myrecord;

EXIT WHEN mycursor%NOTFOUND;

DBMS_OUTPUT.PUT_LINE('deptNum='||myrecord.deptno||' deptName='||myrecord.dname);

END LOOP;

CLOSE mycursor;

END;



FOR循环操作游标

使用FOR循环读取游标时,不需要显示申明变量用于接收结果,也不需要手动打开和关闭游标,例如:

DECLARE

CURSOR mycursor(num varchar2) IS

SELECT * FROM DEPT WHERE deptno=num;

BEGIN

FOR cur IN mycursor(10) LOOP

DBMS_OUTPUT.PUT_LINE('deptNum='||cur.deptno||' deptName='||cur.dname);

END LOOP;

END;



注意:PL/SQL中参数只需要给出类型,不需要给出长度或精度。

当直接将游标的值读取到变量时,变量的个数应与游标指向的结果集的列数相同。例如结果集中有两个列,,那么使用FETCH....INTO 时对应的变量个数也应该有两个。

DECLARE

d_no number;

d_name varchar2(10);

CURSOR mycursor(num varchar2) IS

SELECT deptno,dname FROM DEPT WHERE deptno=num;

BEGIN

OPEN mycursor(10);

FETCH mycursor INTO d_no,d_name;

LOOP

DBMS_OUTPUT.PUT_LINE(d_no||' '||d_name);

FETCH mycursor INTO d_no,d_name;

EXIT WHEN mycursor%NOTFOUND;

END LOOP;

CLOSE mycursor;

END;

/



%ROWCOUNT初始值为null,每当使用FETCH...INTO从游标中取出一条数据后, ROWCOUNT的值加1,并不是标识结果集的行数。

例如:

DECLARE

d_name varchar2(10);

CURSOR mycursor IS

SELECT dname FROM DEPT;

BEGIN

OPEN mycursor;

LOOP

FETCH mycursor INTO d_name;

EXIT WHEN mycursor%NOTFOUND;

DBMS_OUTPUT.PUT_LINE(mycursor%ROWCOUNT);

END LOOP;

CLOSE mycursor;

END;

结果集中有4行记录,输出结果为:1 2 3 4



可更新数据的游标

要想在使用游标的同时修改数据,需要在申明游标时加上FOR UPDATE关键字。

例如:

DECLARE

d_name VARCHAR2(20);

CURSOR mycursor IS

SELECT dname FROM dept FOR UPDATE;

BEGIN

OPEN mycursor;

LOOP

FETCH mycursor INTO d_name;

EXIT WHEN mycursor%NOTFOUND;

UPDATE dept SET dname=RTRIM(dname,'_t') WHERE CURRENT OF mycursor;

END LOOP;

CLOSE mycursor;

END;

CURRENT OF+游标名:获取游标当前所指向的行

RTRIM(dname,'_t'):LTRIM、RTRIM实现字符串过滤(不仅仅去除空格)





隐式游标:不使用DECLARE显示申明的游标。

例如:

BEGIN

FOR cur IN(SELECT dname FROM dept) LOOP

DBMS_OUTPUT.PUT_LINE(cur.dname);

END LOOP;

END;



1、含有参数的游标

declare
cursor cur_my (mv number) is select * from Person where no begin
for tem in cur_my(4) loop
DBMS_OUTPUT.put_line('name:'||tem.name);
end loop;
end;

2、设置引用游标
declare
temp_row Person%rowtype;
type my_type is ref cursor;
cur_my my_type;
begin
open cur_my for 'select * from Person ';
loop
fetch cur_my into temp_row;
exit when cur_my%notfound;
DBMS_OUTPUT.put_line('name:'||temp_row.name);
end loop;
close cur_my;
end;

3、for loop循环游标

DECLARE
v_id Integer;
v_name varchar2(50);
v_age Integer;
cursor cur_mycursor is select id,name,age from Users;
BEGIN
for temp in cur_mycursor loop
v_id :=temp.id;
v_name :=temp.name;
v_age :=temp.age;
dbms_output.put_line('id:'||v_id||'name:'||v_name||'age:'||v_age);
end loop;
/**dbms_output.put_line('所有记录数:'||cur_mycursor%rowcount||'条!');*/
END;

4、标准化loop循环游标

DECLARE
v_id Integer;
v_name varchar2(50);
v_age Integer;
cursor cur_mycursors is select id,name,age from Users;
BEGIN
OPEN cur_mycursors;
dbms_output.put_line('所有记录数:'||cur_mycursors%rowcount||'条!');
LOOP
FETCH cur_mycursors INTO v_id,v_name,v_age;
dbms_output.put_line('id:'||v_id||'name:'||v_name||'age:'||v_age);
IF cur_mycursors%NOTFOUND THEN
EXIT;
END IF;
END LOOP;
dbms_output.put_line('所有记录数:'||cur_mycursors%rowcount||'条!');
CLOSE cur_mycursors;
END;

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