【REF CURSOR 小结】
 
 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。

 


(1)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


(2)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

 

(3)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