oracle 游标变量ref cursor详解

一 介绍

     像游标cursor一样，游标变量ref cursor指向指定查询结果集当前行。游标变量显得更加灵活因为其声明并不绑定指定查询。

其主要运用于PLSQL函数或存储过程以及其他编程语言java等程序之间作为参数传递。

    不像游标的一点，游标变量没有参数。

    游标变量具有以下属性：

    (%FOUND, %NOTFOUND, %ISOPEN, and %ROWCOUNT)

二 用法介绍：

1、声明格式：

DECLARE

TYPE DeptCurTyp IS REF CURSOR RETURN departments%ROWTYPE;

2、游标变量又分为强类型strong(with a return type)和弱类型(with no return type)：

DECLARE
   TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE; -- 强类型
   TYPE genericcurtyp IS REF CURSOR; -- 弱类型
   cursor1 empcurtyp;
   cursor2 genericcurtyp;
   my_cursor SYS_REFCURSOR; -- 使用预定义游标变量sys_refcursor
   TYPE deptcurtyp IS REF CURSOR RETURN departments%ROWTYPE;
   dept_cv deptcurtyp; -- 声明游标变量

或是返回record类型：

DECLARE
   TYPE EmpRecTyp IS RECORD (
   employee_id NUMBER,
   last_name VARCHAR2(25),
   salary NUMBER(8,2));
   TYPE EmpCurTyp IS REF CURSOR RETURN EmpRecTyp;
   emp_cv EmpCurTyp; -- declare cursor variable

3、使用游标变量作为参数传递：

DECLARE
TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;
emp empcurtyp;
-- after result set is built, process all the rows inside a single procedure
-- rather than calling a procedure for each row
PROCEDURE process_emp_cv (emp_cv IN empcurtyp) IS
person employees%ROWTYPE;
BEGIN
DBMS_OUTPUT.PUT_LINE('-----');
DBMS_OUTPUT.PUT_LINE('Here are the names from the result set:');
LOOP
FETCH emp_cv INTO person;
EXIT WHEN emp_cv%NOTFOUND;
DBMS_OUTPUT.PUT_LINE('Name = ' || person.first_name ||
' ' || person.last_name);
END LOOP;
END;
BEGIN
-- First find 10 arbitrary employees.
OPEN emp FOR SELECT * FROM employees WHERE ROWNUM < 11;
process_emp_cv(emp);
CLOSE emp;
-- find employees matching a condition.
OPEN emp FOR SELECT * FROM employees WHERE last_name LIKE 'R%';
process_emp_cv(emp);
CLOSE emp;
END;
/

4、使用游标熟悉检查游标变量是否打开

DECLARE
TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;
emp_cv empcurtyp;
BEGIN
IF NOT emp_cv%ISOPEN THEN -- open cursor variable
OPEN emp_cv FOR SELECT * FROM employees;
END IF;
CLOSE emp_cv;
END;
/

5、在包package中声明游标变量：

CREATE PACKAGE emp_data AS
TYPE empcurtyp IS REF CURSOR RETURN employees%ROWTYPE;
PROCEDURE open_emp_cv (emp_cv IN OUT empcurtyp);
END emp_data;
/
CREATE PACKAGE BODY emp_data AS
PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp) IS
BEGIN
OPEN emp_cv FOR SELECT * FROM employees;
END open_emp_cv;
END emp_data;
/

6、提取游标变量到集合类型collection：

DECLARE
TYPE empcurtyp IS REF CURSOR;
TYPE namelist IS TABLE OF employees.last_name%TYPE;
TYPE sallist IS TABLE OF employees.salary%TYPE;
emp_cv empcurtyp;
names namelist;
sals sallist;
BEGIN
OPEN emp_cv FOR SELECT last_name, salary FROM employees
WHERE job_id = 'SA_REP';
FETCH emp_cv BULK COLLECT INTO names, sals;
CLOSE emp_cv;
-- loop through the names and sals collections
FOR i IN names.FIRST .. names.LAST
LOOP
DBMS_OUTPUT.PUT_LINE('Name = ' || names(i) || ', salary = ' || sals(i));
END LOOP;
END;
/

三 游标变量的使用限制：

1、不能再包说明中声明游标变量；

2、不能用“=”运算符比较游标变量相等性、不等性及是否为空；

3、不能存储于表列中；

4、不能将游标变量存在于关联数组、嵌套表或数组；

5、游标和游标变量之前是不可互操作的！

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附：

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1、强类型游标：

CREATE OR REPLACE PACKAGE strongly_typed IS

TYPE return_cur IS REF CURSOR RETURN all_tables%ROWTYPE;
PROCEDURE child(p_return_rec OUT return_cur);
PROCEDURE parent(p_NumRecs PLS_INTEGER);

END strongly_typed;
/

CREATE OR REPLACE PACKAGE BODY strongly_typed IS
PROCEDURE child(p_return_rec OUT return_cur) IS

BEGIN
  OPEN p_return_rec FOR
  SELECT * FROM all_tables;
END child;
--==================================================
PROCEDURE parent (p_NumRecs PLS_INTEGER) IS
 p_retcur return_cur;
 at_rec   all_tables%ROWTYPE;
BEGIN
  child(p_retcur);

  FOR i IN 1 .. p_NumRecs
  LOOP
    FETCH p_retcur
    INTO at_rec;

    dbms_output.put_line(at_rec.table_name ||
    ' - ' || at_rec.tablespace_name ||
    ' - ' || TO_CHAR(at_rec.initial_extent) ||
    ' - ' || TO_CHAR(at_rec.next_extent));
  END LOOP;
END parent;
END strongly_typed;
/

set serveroutput on

exec strongly_typed.parent(1);
exec strongly_typed.parent(8);

2、弱类型游标：

CREATE OR REPLACE PROCEDURE child (
 p_NumRecs IN PLS_INTEGER,
 p_return_cur OUT SYS_REFCURSOR)
IS

BEGIN
  OPEN p_return_cur FOR
  'SELECT * FROM all_tables WHERE rownum <= ' || p_NumRecs ;
END child;
/

CREATE OR REPLACE PROCEDURE parent (pNumRecs VARCHAR2) IS
 p_retcur  SYS_REFCURSOR;
 at_rec    all_tables%ROWTYPE;
BEGIN
  child(pNumRecs, p_retcur);

  FOR i IN 1 .. pNumRecs
  LOOP
    FETCH p_retcur
    INTO at_rec;

    dbms_output.put_line(at_rec.table_name ||
    ' - ' || at_rec.tablespace_name ||
    ' - ' || TO_CHAR(at_rec.initial_extent) ||
    ' - ' || TO_CHAR(at_rec.next_extent));
  END LOOP;
END parent;
/

set serveroutput on

exec parent(1);
exec parent(17);

3、预定义游标变量：

CREATE TABLE employees (
empid   NUMBER(5),
empname VARCHAR2(30));

INSERT INTO employees (empid, empname) VALUES (1, 'Dan Morgan');
INSERT INTO employees (empid, empname) VALUES (2, 'Hans Forbrich');
INSERT INTO employees (empid, empname) VALUES (3, 'Caleb Small');
COMMIT;
CREATE OR REPLACE PROCEDURE pass_ref_cur(p_cursor SYS_REFCURSOR) IS

TYPE array_t IS TABLE OF VARCHAR2(4000)
INDEX BY BINARY_INTEGER;

rec_array array_t;

BEGIN
  FETCH p_cursor BULK COLLECT INTO rec_array;

  FOR i IN rec_array.FIRST .. rec_array.LAST
  LOOP
    dbms_output.put_line(rec_array(i));
  END LOOP;
END pass_ref_cur;
/
set serveroutput on

DECLARE
 rec_array SYS_REFCURSOR;
BEGIN
  OPEN rec_array FOR
  'SELECT empname FROM employees';

  pass_ref_cur(rec_array);
  CLOSE rec_array;
END;
/

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Dylan    presents.