oracle ref cursor的介绍

利用REF CURSOR，可以在程序间传递结果集（一个程序里打开游标变量，在另外的程序里处理数据）。
也可以利用REF CURSOR实现BULK SQL，提高SQL性能。


REF CURSOR分两种，Strong REF CURSOR 和 Weak REF CURSOR。


Strong REF CURSOR:指定retrun type，CURSOR变量的类型必须和return type一致。
DECLARE
TYPE strongcurtyp IS REF CURSOR RETURN emp%ROWTYPE;
emp_cv strongcurtyp;


Weak REF CURSOR:不指定return type，能和任何类型的CURSOR变量匹配。
DECLARE
TYPE weakcurtyp IS REF CURSOR;
weak_cv weakcurtyp;
any_cv SYS_REFCURSOR; --使用SYS_REFCURSOR可以使变量any_cv跟任何weak REF CURSOR类型匹配。


使用Strong REF CURSOR例子
CREATE OR REPLACE PACKAGE emp_data AS
TYPE empcurtyp IS REF CURSOR RETURN emp%rowtype; --定义TYPE as Strong REF CURSOR
PROCEDURE open_emp_cv(emp_cv IN OUT empcurtyp, choice INT); --根据不同的choice选择不同的CURSOR
PROCEDURE retrieve_data(choice INT); --通过调用procedure open_emp_cv，返回指定的结果集。
END emp_data;


=============================================




CREATE OR REPLACE PACKAGE BODY emp_data AS

--procedure open_emp_cv-----------------------------

PROCEDURE open_emp_cv(emp_cv IN OUT empcurtyp, choice INT) IS --emp_cv作为传入/传出的CURSOR PARAMETER
BEGIN
IF choice = 1 THEN
OPEN emp_cv FOR
SELECT * FROM emp WHERE empno < 7800;
ELSIF choice = 2 THEN
OPEN emp_cv FOR
SELECT * FROM emp WHERE SAL < 1000;
ELSIF choice = 3 THEN
OPEN emp_cv FOR
SELECT * FROM emp WHERE ename like 'J%';
END IF;
END;


--procedure retrieve_data----------------------------------

PROCEDURE retrieve_data(choice INT) IS
return_cv empcurtyp; --定义传入open_emp_cv的CURSOR变量
return_row emp%ROWTYPE;
invalid_choice EXCEPTION;
BEGIN
open_emp_cv(return_cv, choice); --调用 procedure OPEN_EMP_CV

IF choice = 1 THEN
DBMS_OUTPUT.PUT_LINE('EMPLOYEES with empno less than 7800');
ELSIF choice = 2 THEN
DBMS_OUTPUT.PUT_LINE('EMPLOYEES with salary less than 1000');
ELSIF choice = 3 THEN
DBMS_OUTPUT.PUT_LINE('EMPLOYEES with name starts with ''J''');
ELSE
RAISE invalid_choice;
END IF;

LOOP
FETCH return_cv
INTO return_row;
EXIT WHEN return_cv%NOTFOUND;

DBMS_OUTPUT.PUT_LINE(return_row.empno || '--' || return_row.ename || '--' ||
return_row.sal);
END LOOP;

EXCEPTION
WHEN invalid_choice THEN
DBMS_OUTPUT.PUT_LINE('The CHOICE should be in one of (1,2,3)!');
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('Errors in procedure RETRIEVE_DATA!');
END;

END emp_data;


================================




执行：
SQL> EXEC emp_data.retrieve_data(1);
EMPLOYEES with empno less than 7800
7369--SMITH--800
7499--ALLEN--1600
7521--WARD--1250
7566--JONES--2975
7654--MARTIN--1250
7698--BLAKE--2850
7782--CLARK--2450
7788--SCOTT--3000
PL/SQL procedure successfully completed

SQL> EXEC emp_data.retrieve_data(2);
EMPLOYEES with salary less than 1000
7369--SMITH--800
7900--JAMES--950
PL/SQL procedure successfully completed

SQL> EXEC emp_data.retrieve_data(3);
EMPLOYEES with name starts with 'J'
7566--JONES--2975
7900--JAMES--950
PL/SQL procedure successfully completed

SQL> EXEC emp_data.retrieve_data(34);
The CHOICE should be in one of (1,2,3)!
PL/SQL procedure successfully completed



使用Weak REF CURSOR例子
--procedure open_cv---------------------------------------

create or replace procedure open_cv(choice IN INT,
return_cv OUT SYS_REFCURSOR) is
--参数return_cv为weak REF CURSOR,利用SYS_CURSOR来定义
begin
if choice = 1 then
open return_cv for 'select * from emp';
elsif choice = 2 then
open return_cv for 'select * from dept';
end if;
end open_cv;


--procedure retrieve_data------------------------------------

create or replace procedure retrieve_data(choice IN INT) is
emp_rec emp%rowtype;
dept_rec dept%rowtype;
return_cv SYS_REFCURSOR;
invalid_choice exception;
begin
if choice=1 then
dbms_output.put_line('employee information');
open_cv(1,return_cv); --调用procedure open_cv;
loop
fetch return_cv into emp_rec;
exit when return_cv%notfound;
dbms_output.put_line(emp_rec.empno||'-'||emp_rec.ename||'-'||emp_rec.sal);
end loop;
elsif choice=2 then
dbms_output.put_line('department information');
open_cv(2,return_cv);
loop
fetch return_cv into dept_rec;
exit when return_cv%notfound;
dbms_output.put_line(dept_rec.deptno||'-'||dept_rec.dname||'-'||dept_rec.loc);
end loop;
else
raise invalid_choice;
end if;

exception
when invalid_choice then
dbms_output.put_line('The CHOICE should be one of 1 and 2!');
when others then
dbms_output.put_line('Errors in procedure retrieve_data');
end retrieve_data;

-----------------------------------------------------------------

执行：
SQL> exec retrieve_data(1);
employee information
7369-SMITH-800
7499-ALLEN-1600
7521-WARD-1250
7566-JONES-2975
7654-MARTIN-1250
7698-BLAKE-2850
......
PL/SQL procedure successfully completed

SQL> exec retrieve_data(2);
department information
10-ACCOUNTING-NEW YORK
20-RESEARCH-DALLAS
30-SALES-CHICAGO
40-OPERATIONS-BOSTON
PL/SQL procedure successfully completed



用REF CURSOR实现BULK功能
1. To speed up INSERT, UPDATE, and DELETE statements, enclose the SQL statement within a PL/SQL FORALL statement instead of a loop construct.
2. To speed up SELECT statements, include the BULK COLLECT INTO clause in the SELECT statement instead of using INTO.



SQL> create table tab2 as select empno ID, ename NAME, sal SALARY from emp where 1=2;
Table created


-------------------------------------------------------

create or replace procedure REF_BULK is
type empcurtyp is ref cursor;
type idlist is table of emp.empno%type;
type namelist is table of emp.ename%type;
type sallist is table of emp.sal%type;

emp_cv empcurtyp;
ids idlist;
names namelist;
sals sallist;

row_cnt number;
begin
open emp_cv for
select empno, ename, sal from emp;
fetch emp_cv BULK COLLECT
INTO ids, names, sals; --BULK COLLECT INTO instead of INTO
close emp_cv;

for i in ids.first .. ids.last loop
dbms_output.put_line('id=' || ids(i) || ' name=' || names(i) ||
' salary=' || sals(i));
end loop;

forall i in ids.first .. ids.last --FORALL instead of FOR ...LOOP
insert into tab2 values (ids(i), names(i), sals(i));
commit;

select count(*) into row_cnt from tab2;
dbms_output.put_line('-----------------------------------');
dbms_output.put_line('The row number of tab2 is ' || row_cnt);
end REF_BULK;


------------------------------------------------------------

执行：

SQL> exec ref_bulk;

id=7369 name=SMITH salary=800
id=7499 name=ALLEN salary=1600
id=7521 name=WARD salary=1250
id=7566 name=JONES salary=2975
id=7654 name=MARTIN salary=1250
id=7698 name=BLAKE salary=2850
id=7782 name=CLARK salary=2450
id=7788 name=SCOTT salary=3000
id=7839 name=KING salary=5000
id=7844 name=TURNER salary=1500
id=7876 name=ADAMS salary=1100
id=7900 name=JAMES salary=950
id=7902 name=FORD salary=3000
id=7934 name=MILLER salary=1300
-----------------------------------
The row number of tab2 is 14

PL/SQL procedure successfully completed