oracle 笔记 VI 之游标 (CURSOR)

游标(CURSOR),很重要

游标:用于处理多行记录的事务
游标是一个指向上下文的句柄(handle)或指针,简单说，游标就是一个指针

1 处理显式游标
显式游标处理需 4个 PL/SQL 步骤,显示游标主要用于处理查询语句
(1) 定义游标
格式: CURSOR cursor_name [(partment[,parameter]...)] IS select_statement;
定义的游标不能有 INTO 子句
(2) 打开游标
OPEN cursor_name[...];
PL/SQL 程序不能用 OPEN 语句重复打开一个游标
(3)提取游标数据
FETCH cursor_name INTO {variable_list | record_variable};
(4) 关闭游标
CLOSE cursor_name;



例 1 查询前 10 名员工的信息
declare
--定义游标
cursor c_cursor is select last_name,salary from employees where rownum < 11 order by salary;
v_name employees.last_name%type;
V_sal employees.salary%type;

begin
--打开游标
open c_cursor;
-- 提取游标数据
fetch c_cursor into v_name,v_sal;

while c_cursor %found loop
dbms_output.put_line(v_name || ':' || v_sal);
fetch c_cursor into v_name,v_sal;
end loop;

--关闭游标
close c_cursor;
end;



----------------------------------
练习: 输入部门号 dep_id,查询该部门的平均工资 : avg_sal,员工工资为 salary
若 salary < avg_sal - 500 工资涨 500
若 avg_sal - 500 <= salary < avg_sal + 500 工资涨 300
若 avg_sal + 500 <= salary 工资涨 100;

declare
--存放平均工资
avg_sal employees.salary%type;
-- 存放每个员工的工资
sal employees.salary%type;
--存放输入的department_id
dep_id employees.department_id%type := &dep_id;
--存放员工 employee_id 的记录
emp_id employees.employee_id%type;


--定义游标
cursor emp_cursor is select employee_id,salary from employees where department_id = dep_id;
begin
select avg(salary) into avg_sal from employees where department_id = dep_id;

open emp_cursor;
fetch emp_cursor into emp_id,sal;

--循环操作
while emp_cursor%found loop
dbms_output.put_line(emp_id || ', ' || sal);
if sal < avg_sal -500 then
sal := sal + 500;
elsif sal < avg_sal - 500 then
sal := sal +300;
else
sal := sal +100;
end if;
update employees set salary = sal where employee_id =emp_id;
fetch emp_cursor into emp_id,sal;

end loop;

close emp_cursor;
end



游标的for循环:

declare
avg_sal employees.salary%type;

sal employees.salary%type;

dep_id employees.department_id%type := &dep_id;

cursor emp_cursor(v_dep_id number default 30) is select employee_id,salary
from employees where department_id = v_dep_id;
begin

select avg(salary) into avg_sal from employees where department_id = dep_id;

--游标的 for 循环免除如下操作:1.打开游标 2.关闭游标 3.提取游标数据 4.定义存放游标每一条记录的数据结构(通常为 record)
for emp_record in emp_cursor(v_dep_id => dep_id) loop
--dbms_output.put_line(emp_record.employee_id || ',' || emp_record.salary);
sal := emp_record.salary;

--确定涨后的工资是多少
if sal < avg_sal - 500 then
sal := sal + 500;
elsif sal <avg_sal + 500 then
sal := sal +300;
else
sal := sal +100;
end if;

--更新操作
update employees set salary = sal where employee_id = emp_record.employee_id;
end loop;



2 处理隐式游标,主要用于处理修改、删除语句
由系统隐含创建的游标称为隐式游标，隐式游标的名字为 SQL

3 游标修改和删除
指在游标定位下，修改或删除表中指定的数据行