Oracle管道函数(Pipelined Table Function)简介

Oracle管道函数(Pipelined Table Function)简介

1、概述：

一、管道函数便是能够返回行集合（可使嵌套表nestedtable或数组varray）的函数，咱们能够像查询物理表同样查询它或者将其赋值给集合变量。
   二、管道函数为并行执行，在普通的函数中使用dbms_output输出的信息，须要在服务器执行完整个函数后一次性的返回给客户端。若是须要在客户端实时的输出函数执行过程当中的一些信息，在oracle9i之后可使用管道函数(pipelinefunction)。
  3 、关键字PIPELINED代表这是一个Oracle管道函数，oracle管道函数的返回值类型必须为集合，在函数中，PIPEROW语句被用来返回该集合的单个元素，函数以一个空的RETURN语句结束，以代表它已经完成。
 四、因为管道函数的并发多管道流式设计以及实时返回查询结果而去除了中间环节所以能够带来可观的性能提高。

2、如何编写管道函数：

例1：
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CREATE OR REPLACE PACKAGE pkg1 AS

TYPE numset_t IS TABLE NUMBER;  
FUNCTION f1(x NUMBER) RETURN numset_t PIPELINED;

END pkg1;

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CREATE OR REPLACE PACKAGE BODY pkg1 AS

FUNCTION f1(x NUMBER) RETURN numset_t PIPELINED IS 
    BEGIN 
        FOR i IN 1..x LOOP  
            PIPE ROW(i);  
        END LOOP;  
        RETURN;  
    END;

END pkg1;

运行：
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1
SELECT * FROM TABLE(pkg1.f1(5));

结果：
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COLUMN_VALUE

1
       2
       3
       4
       5

3、管道函数用于数据转换：

例2：

管道函数能够和常规函数同样接收任何参数，下面的管道函数中参数为ref cursor。

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CREATE OR REPLACE PACKAGE refcur_pkg IS
TYPE refcur_t IS REF CURSOR RETURN emp%ROWTYPE;
TYPE outrec_typ IS RECORD (

var_num    NUMBER(6),  
var_char1  VARCHAR2(30),  
var_char2  VARCHAR2(30));

TYPE outrecset IS TABLE OF outrec_typ;
FUNCTION f_trans(p refcur_t)

RETURN outrecset PIPELINED;

END refcur_pkg;

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CREATE OR REPLACE PACKAGE BODY refcur_pkg IS
FUNCTION f_trans(p refcur_t)
RETURN outrecset PIPELINED IS

out_rec outrec_typ;  
in_rec  p%ROWTYPE;

BEGIN
LOOP

FETCH p INTO in_rec;  
EXIT WHEN p%NOTFOUND;  
-- first row  
out_rec.var_num := in_rec.empno;  
out_rec.var_char1 := in_rec.ename;  
out_rec.var_char2 := in_rec.mgr;  
PIPE ROW(out_rec);  
-- second row  
out_rec.var_num := in_rec.deptno;  
out_rec.var_char1 := in_rec.deptno;  
out_rec.var_char2 := in_rec.job;  
PIPE ROW(out_rec);

END LOOP;
CLOSE p;
RETURN;
END;
END refcur_pkg;

运行：
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SELECT FROM TABLE(refcur_pkg.f_trans(CURSOR(SELECT FROM emp WHERE empno=7782)));

结果：
VAR_NUM VAR_CHAR1 VAR_CHAR2

---

7782               CLARK                          7839
    10                   10                          MANAGER

4、用法扩展：

一、表函数间传递数据：

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SELECT FROM TABLE(f(CURSOR(SELECT FROM TABLE(g()))));

二、使用游标变量接收管道函数返回的结果：

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OPEN c FOR SELECT * FROM TABLE(f(...));

三、使用多个游标变量入参：
        例3：Oac_no_warn代码

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-- Define the ref cursor types
CREATE PACKAGE refcur_pkg IS
TYPE refcur_t1 IS REF CURSOR RETURN employees%ROWTYPE;
TYPE refcur_t2 IS REF CURSOR RETURN departments%ROWTYPE;
TYPE outrec_typ IS RECORD (

var_num    NUMBER(6),  
var_char1  VARCHAR2(30),  
var_char2  VARCHAR2(30));

TYPE outrecset IS TABLE OF outrec_typ;
FUNCTION g_trans(p1 refcur_t1, p2 refcur_t2)

RETURN outrecset PIPELINED;

END refcur_pkg;
/

CREATE PACKAGE BODY refcur_pkg IS
FUNCTION g_trans(p1 refcur_t1, p2 refcur_t2)

RETURN outrecset PIPELINED IS 
out_rec outrec_typ;  
in_rec1 p1%ROWTYPE;  
in_rec2 p2%ROWTYPE;

BEGIN
LOOP

FETCH p2 INTO in_rec2;  
EXIT WHEN p2%NOTFOUND;

END LOOP;
CLOSE p2;
LOOP

FETCH p1 INTO in_rec1;  
EXIT WHEN p1%NOTFOUND;  
-- first row  
out_rec.var_num := in_rec1.employee_id;  
out_rec.var_char1 := in_rec1.first_name;  
out_rec.var_char2 := in_rec1.last_name;  
PIPE ROW(out_rec);  
-- second row  
out_rec.var_num := in_rec2.department_id;  
out_rec.var_char1 := in_rec2.department_name;  
out_rec.var_char2 := TO_CHAR(in_rec2.location_id);  
PIPE ROW(out_rec);

END LOOP;
CLOSE p1;
RETURN;
END;
END refcur_pkg;
/

-- SELECT query using the g_trans table function
SELECT * FROM TABLE(refcur_pkg.g_trans(
CURSOR(SELECT * FROM employees WHERE department_id = 60),
CURSOR(SELECT * FROM departments WHERE department_id = 60)));

四、管道函数做为聚合函数使用：

例4：Oac_no_warn代码

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CREATE TABLE gradereport (student VARCHAR2(30), subject VARCHAR2(30),

weight NUMBER, grade NUMBER);

INSERT INTO gradereport VALUES('Mark', 'Physics', 4, 4);
INSERT INTO gradereport VALUES('Mark','Chemistry', 4, 3);
INSERT INTO gradereport VALUES('Mark','Maths', 3, 3);
INSERT INTO gradereport VALUES('Mark','Economics', 3, 4);

CREATE PACKAGE pkg_gpa IS
TYPE gpa IS TABLE OF NUMBER;
FUNCTION weighted_average(input_values SYS_REFCURSOR)

RETURN gpa PIPELINED;

END pkg_gpa;
/
CREATE PACKAGE BODY pkg_gpa IS
FUNCTION weighted_average(input_values SYS_REFCURSOR)
RETURN gpa PIPELINED IS
grade NUMBER;
total NUMBER := 0;
total_weight NUMBER := 0;
weight NUMBER := 0;
BEGIN
-- The function accepts a ref cursor and loops through all the input rows
LOOP

FETCH input_values INTO weight, grade;  
 EXIT WHEN input_values%NOTFOUND;

-- Accumulate the weighted average

total_weight := total_weight + weight;  
 total := total + grade*weight;

END LOOP;
PIPE ROW (total / total_weight);
RETURN; -- the function returns a single result
END;
END pkg_gpa;
/
-- the query result comes back as a nested table with a single row
-- COLUMN_VALUE is a keyword that returns the contents of a nested table
SELECT w.column_value "weighted result" FROM TABLE(

pkg_gpa.weighted_average(CURSOR(SELECT weight, grade FROM gradereport))) w;

五、在管道函数中进行DML操做,咱们使用自治事务使管道函数做为独立事务处理：
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CREATE FUNCTION f(p SYS_REFCURSOR)
RETURN CollType PIPELINED IS

PRAGMA AUTONOMOUS_TRANSACTION;

BEGIN
NULL;
END;
/

六、对管道函数进行DML操做：

实际上咱们没法直接对管道函数进行DML操做，例如如下语句都会失败：

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UPDATE F(CURSOR(SELECT * FROM tab)) SET col = value;
INSERT INTO f(...) VALUES ('any', 'thing');

官方给出的方案是建立一个基于管道函数的VIEW，而后在这个VIEW上建立相应的instead of 触发器。下面给出操做实例：
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CREATE OR REPLACE VIEW V_F_TRANS AS
SELECT x.var_num, x.var_char1, x.var_char2
FROM TABLE(refcur_pkg.f_trans(CURSOR (SELECT *

FROM emp))) x;

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CREATE OR REPLACE TRIGGER tri_f_trans INSTEAD OF INSERT ON v_f_trans FOR EACH ROW BEGIN dbms_output.put_line('Trigger of a pipelined funtion based view was on fire!'); END;