oracle 游标用法详解
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 * from Person where no
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;