3、关键字PIPELINED表明这是一个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，PIPE ROW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，以表明它已经完成。

4、由于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因此可以带来可观的性能提升。

二、如何编写管道函数：

CREATE OR REPLACE PACKAGE pkg1 AS
    TYPE numset_t IS TABLE NUMBER;
    FUNCTION f1(x NUMBER) RETURN numset_t PIPELINED;
END pkg1;

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;

SELECT * FROM TABLE(pkg1.f1(5));

三 管道函数用于数据转换：

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;

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;

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