Oracle Cursor用法总结
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cursor分为三种，一是直接声明为cursor变量，二是首先声明类型再声明变量，三是声明为sys_refcursor。
（1）直接声明
declare
cursor emp_cur is select * from emp;
emp_record emp%rowtype;
begin
open emp_cur;
loop
fetch emp_cur into emp_record;
exit when emp_cur%notfound;
dbms_output.put_line(‘name is:‘ || emp_record.ename ||‘ and sal is:‘ || emp_record.sal);
end loop;
close emp_cur;
end;
/
(2)ref cursor:分为强类型（有return子句的）和弱类型，强类型在使用时，其返回类型必须和return中的类型一致，否则报错，而弱类型可以随意打开任何类型。
例如：
强类型
declare
type emp_cur_type is ref cursor return emp%rowtype;
emp_cur emp_cur_type;
emp_record emp%rowtype;
begin
open emp_cur for select * from emp;
loop
fetch emp_cur into emp_record;
exit when emp_cur%notfound;
dbms_output.put_line(‘name is:‘ || emp_record.ename || ‘ and sal is:‘ || emp_record.sal);
end loop;
close emp_cur;
--open emp_cur for select * from dept; 错误的，类型不一致。
--close emp_cur;
end;
/
弱类型：
declare
type emp_cur_type is ref cursor;
emp_cur emp_cur_type;
emp_record emp%rowtype;
dept_record dept%rowtype;
begin
open emp_cur for select * from emp;
loop
fetch emp_cur into emp_record;
exit when emp_cur%notfound;
dbms_output.put_line(‘name is:‘ || emp_record.ename || ‘ and sal is:‘ || emp_record.sal);
end loop;
close emp_cur;
open emp_cur for select * from dept; --可再次打开，不同类型的
loop
fetch emp_cur into dept_record;
exit when emp_cur%notfound;
dbms_output.put_line(‘dname is:‘ || dept_record.dname);
end loop;
close emp_cur;
end;
/
（3）sys_refcursor:可多次打开，直接声明此类型的变量，不用先定义类型再声明变量。
declare
emp_cur sys_refcursor;
emp_record emp%rowtype;
dept_record dept%rowtype;
begin
open emp_cur for select * from emp;
loop
fetch emp_cur into emp_record;
exit when emp_cur%notfound;
dbms_output.put_line(‘name is:‘ || emp_record.ename || ‘ and sal is:‘ || emp_record.sal);
end loop;
close emp_cur;
open emp_cur for select * from dept; --可再次打开，不同类型的
loop
fetch emp_cur into dept_record;
exit when emp_cur%notfound;
dbms_output.put_line(‘dname is:‘ || dept_record.dname);
end loop;
close emp_cur;
end;
/
其他总结：
1、游标可以用for循环，但只限于cursor cur_var is ……这种类型，用在其他的里面都是错误的；for本身就包含了打开、关闭游标，此时再显示打开关闭都是错误的。
declare
cursor emp_cur is select * from emp;
begin
--open emp_cur; 是错误的，因为for本身就包含了打开、关闭
for emp_record in emp_cur
loop
dbms_output.put_line(‘name is:‘ || emp_record.ename || ‘ and sal is:‘ || emp_record.sal);
end loop;
--close emp_cur; 是错误的，for本身包含了关闭。
end;
--是不是表示：ref cursor变量不支持for打开并循环？
declare
type emp_cur_type is ref cursor return emp%rowtype;
emp_cur emp_cur_type;
begin
open emp_cur for select * from emp;--怎么都是错，for已经打开了。
for emp_record in emp_cur -- 不管前面有没有打开语句，for都不承认这种类型
loop
dbms_output.put_line(‘name is:‘ || emp_record.ename || ‘ and sal is:‘ || emp_record.sal);
end loop;
end;
2、游标可以带参数
DECLARE
CURSOR c1 (job VARCHAR2, max_wage NUMBER) IS
SELECT * FROM employees WHERE job_id = job AND salary > max_wage;
BEGIN
FOR person IN c1(‘CLERK‘, 3000)
LOOP
DBMS_OUTPUT.PUT_LINE(‘Name = ‘ || person.last_name || ‘, salary = ‘ ||
person.salary || ‘, Job Id = ‘ || person.job_id );
END LOOP;
END;
3、bulk collect批量赋值
declare
type emp_cur_type is ref cursor;
emp_cur emp_cur_type;
type name_list is table of emp.ename%type;
type sal_list is table of emp.sal%type;
names name_list;
sals sal_list;
begin
open emp_cur for select ename,sal from emp;
fetch emp_cur bulk collect into names,sals;
close emp_cur;
for i in names.first .. names.last
loop
dbms_output.put_line(‘name is:‘||names(i)||‘ and sal is:‘||sals(i));
end loop;
end;
/
4、cursor变量的位置
CREATE PACKAGE emp_data AS
TYPE EmpCurTyp IS REF CURSOR RETURN employees%ROWTYPE;
-- emp_cv EmpCurTyp; -- not allowed
PROCEDURE open_emp_cv;
END emp_data;
/
CREATE PACKAGE BODY emp_data AS
-- emp_cv EmpCurTyp; -- not allowed
PROCEDURE open_emp_cv IS
emp_cv EmpCurTyp; -- this is legal
BEGIN
OPEN emp_cv FOR SELECT * FROM employees;
END open_emp_cv;
END emp_data;
/
5、嵌套cursor
打开父cursor时，子cursor隐含打开；当
语法格式:cursor(subquery)
A nested cursor is implicitly opened when the containing row is fetched from the parent cursor.
The nested cursor is closed only when:
The nested cursor is explicitly closed by the user
The parent cursor is reexecuted
The parent cursor is closed
The parent cursor is canceled
示例；
declare
type emp_cur_type is ref cursor ;
type dept_cur_type is ref cursor ;
v_ename emp.ename%type;
v_dname dept.dname%type;
emp_cur emp_cur_type;
dept_cur dept_cur_type;
begin
open dept_cur for
select d.dname,
cursor(select e.ename from emp e where e.deptno=d.deptno )emps
from dept d;
loop
fetch dept_cur into v_dname,emp_cur;
exit when dept_cur%notfound;
dbms_output.put_line(‘dname is : ‘||v_dname);
loop
fetch emp_cur into v_ename;
exit when emp_cur%notfound;
dbms_output.put_line(‘--ename is : ‘||v_ename);
end loop;
end loop;
close dept_cur;
end;
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