Create the implementation package named skip_col_pkg containing the DESCRIBE function for the skip_col polymorphic table function (PTF).

CREATE PACKAGE skip_col_pkg AS  
  
  -- OVERLOAD 1: Skip by name --  
  FUNCTION skip_col(tab TABLE,   
                    col columns)  
           RETURN TABLE PIPELINED ROW POLYMORPHIC USING skip_col_pkg;  
  
  FUNCTION describe(tab IN OUT dbms_tf.table_t,   
                    col        dbms_tf.columns_t)  
           RETURN dbms_tf.describe_t;  
  
  -- OVERLOAD 2: Skip by type --  
  FUNCTION skip_col(tab       TABLE,   
                    type_name VARCHAR2,  
                    flip      VARCHAR2 DEFAULT 'False')   
           RETURN TABLE PIPELINED ROW POLYMORPHIC USING skip_col_pkg;  
  
  FUNCTION describe(tab       IN OUT dbms_tf.table_t,   
                    type_name        VARCHAR2,   
                    flip             VARCHAR2 DEFAULT 'False')   
           RETURN dbms_tf.describe_t;  
  
END skip_col_pkg;  

Create the implementation package body which contains the polymorphic table function definition.

CREATE PACKAGE BODY skip_col_pkg AS  
  
/* OVERLOAD 1: Skip by name   
 * NAME:  skip_col_pkg.skip_col   
 * ALIAS: skip_col_by_name  
 *  
 * PARAMETERS:  
 * tab - The input table  
 * col - The name of the columns to drop from the output  
 *  
 * DESCRIPTION:  
 *   This PTF removes all the input columns listed in col from the output  
 *   of the PTF.  
*/   
  FUNCTION  describe(tab IN OUT dbms_tf.table_t,   
                     col        dbms_tf.columns_t)  
            RETURN dbms_tf.describe_t  
  AS   
    new_cols dbms_tf.columns_new_t;  
    col_id   PLS_INTEGER := 1;  
  BEGIN   
    FOR i IN 1 .. tab.column.count() LOOP  
      FOR j IN 1 .. col.count() LOOP  
        tab.column(i).pass_through := tab.column(i).description.name != col(j);  
        EXIT WHEN NOT tab.column(i).pass_through;  
      END LOOP;  
    END LOOP;  
  
    RETURN NULL;  
  END;  
    
 /* OVERLOAD 2: Skip by type  
 * NAME:  skip_col_pkg.skip_col   
 * ALIAS: skip_col_by_type  
 *  
 * PARAMETERS:  
 *   tab       - Input table  
 *   type_name - A string representing the type of columns to skip  
 *   flip      - 'False' [default] => Match columns with given type_name  
 *               otherwise         => Ignore columns with given type_name  
 *  
 * DESCRIPTION:  
 *   This PTF removes the given type of columns from the given table.   
*/   
  
  FUNCTION describe(tab       IN OUT dbms_tf.table_t,   
                    type_name        VARCHAR2,   
                    flip             VARCHAR2 DEFAULT 'False')   
           RETURN dbms_tf.describe_t   
  AS   
    typ CONSTANT VARCHAR2(1024) := upper(trim(type_name));  
  BEGIN   
    FOR i IN 1 .. tab.column.count() LOOP  
       tab.column(i).pass_through :=   
         CASE upper(substr(flip,1,1))  
           WHEN 'F' THEN dbms_tf.column_type_name(tab.column(i).description)!=typ  
           ELSE          dbms_tf.column_type_name(tab.column(i).description) =typ  
         END /* case */;  
    END LOOP;  
  
    RETURN NULL;  
  END;  
  
END skip_col_pkg;  

Create a standalone polymorphic table function named skip_col_by_name for overload 1.

CREATE FUNCTION skip_col_by_name(tab TABLE,   
                                 col columns)  
       RETURN TABLE PIPELINED ROW POLYMORPHIC USING skip_col_pkg; 

Create a standalone polymorphic table function named skip_col_by_type for overload 2.

CREATE FUNCTION skip_col_by_type(tab TABLE,   
                                 type_name VARCHAR2,  
                                 flip VARCHAR2 DEFAULT 'False')  
       RETURN TABLE PIPELINED ROW POLYMORPHIC USING skip_col_pkg; 

SELECT * FROM skip_col_pkg.skip_col(scott.dept, 'number')

SELECT * FROM skip_col_by_type(scott.dept, 'number')

SELECT * FROM skip_col_pkg.skip_col(scott.dept, 'number', flip => 'True')

SELECT *   
FROM skip_col_by_type(scott.dept, 'number', flip => 'True')

SELECT *   
FROM skip_col_by_name(scott.emp, columns(comm, hiredate, mgr))  
WHERE deptno = 20