How to pipeline a function with a dynamic number of columns?

Question

Hi everyone,
I'm trying to figure out how to write a piplined function that generates a dynamic SQL statement from its inputs, executes the query, and returns the results of the query in the pipeline. The number and names of the columns in the dynamic query is unknown number until the function is invoked.
I suspect that DBMS_SQL is involved, but can't quite figure out how to construct a row using it that I can use PIPE ROW on. I also can't figure out what data type the function should return (ANYDATASET?)
pseudo-PLSQL follows:
create function myfunction ( param1 varchar2)
return anydataset pipelined
as
query_string := <... do stuff with param1 ...>
< -- >
open a cursor for query_string
determine the number of columns
read a row
PIPE ROW it
<--->
Can what I'm trying to do be done?
Thanks,
Keith

Answer 1

The following works on 10R2
create or replace type NColPipe as object
  l_parm varchar2(10),   -- The parameter given to the table function
  rows_requested number, -- The parameter given to the table function
  ret_type anytype,      -- The return type of the table function
  rows_returned number,  -- The number of rows currently returned by the table function
  static function ODCITableDescribe( rtype out anytype, p_parm in varchar2, p_rows_req in number := 2 )
  return number,
  static function ODCITablePrepare( sctx out NColPipe, ti in sys.ODCITabFuncInfo, p_parm in varchar2, p_rows_req in number := 2 )
  return number,
  static function ODCITableStart( sctx in out NColPipe, p_parm in varchar2, p_rows_req in number := 2 )
  return number,
  member function ODCITableFetch( self in out NColPipe, nrows in number, outset out anydataset )
  return number,
  member function ODCITableClose( self in NColPipe )
  return number,
  static function show( p_parm in varchar2, p_rows_req in number := 2 )
  return anydataset pipelined using NColPipe
create or replace type body NColPipe as
  static function ODCITableDescribe( rtype out anytype, p_parm in varchar2, p_rows_req in number := 2 )
  return number
  is
    atyp anytype;
  begin
    anytype.begincreate( dbms_types.typecode_object, atyp );
    if p_parm = 'one'
    then
      atyp.addattr( 'one'
                  , dbms_types.typecode_varchar2
                  , null
                  , null
                  , 10
                  , null
                  , null
    elsif p_parm = 'two'
    then
      atyp.addattr( 'one'
                  , dbms_types.typecode_varchar2
                  , null
                  , null
                  , 10
                  , null
                  , null
      atyp.addattr( 'two'
                  , dbms_types.typecode_varchar2
                  , null
                  , null
                  , 10
                  , null
                  , null
    else
      atyp.addattr( p_parm || '1'
                  , dbms_types.typecode_varchar2
                  , null
                  , null
                  , 10
                  , null
                  , null
      atyp.addattr( p_parm || '2'
                  , dbms_types.typecode_varchar2
                  , null
                  , null
                  , 10
                  , null
                  , null
      atyp.addattr( p_parm || '3'
                  , dbms_types.typecode_number
                  , 10
                  , 0
                  , null
                  , null
                  , null
    end if;
    atyp.endcreate;
    anytype.begincreate( dbms_types.typecode_table, rtype );
    rtype.SetInfo( null, null, null, null, null, atyp, dbms_types.typecode_object, 0 );
    rtype.endcreate();
    return odciconst.success;
  exception
    when others then
      return odciconst.error;
  end;  
  static function ODCITablePrepare( sctx out NColPipe, ti in sys.ODCITabFuncInfo, p_parm in varchar2, p_rows_req in number := 2 )
  return number
  is
    elem_typ sys.anytype;
    prec pls_integer;
    scale pls_integer;
    len pls_integer;
    csid pls_integer;
    csfrm pls_integer;
    tc pls_integer;
    aname varchar2(30);
  begin
    tc := ti.RetType.GetAttrElemInfo( 1, prec, scale, len, csid, csfrm, elem_typ, aname );
    sctx := NColPipe( p_parm, p_rows_req, elem_typ, 0 );
    return odciconst.success;
  end;
  static function ODCITableStart( sctx in out NColPipe, p_parm in varchar2, p_rows_req in number := 2 )
  return number
  is
  begin
    return odciconst.success;
  end;
  member function ODCITableFetch( self in out NColPipe, nrows in number, outset out anydataset )
  return number
  is
  begin
    anydataset.begincreate( dbms_types.typecode_object, self.ret_type, outset );
    for i in self.rows_returned + 1 .. self.rows_requested
    loop
      outset.addinstance;
      outset.piecewise();
      if self.l_parm = 'one'
      then
        outset.setvarchar2( to_char( i ) );
      elsif self.l_parm = 'two'
      then
        outset.setvarchar2( to_char( i ) );
        outset.setvarchar2( 'row: ' || to_char( i ) );
      else
        outset.setvarchar2( 'row: ' || to_char( i ) );
        outset.setvarchar2( 'row: ' || to_char( i ) );
        outset.setnumber( i );
      end if;
      self.rows_returned := self.rows_returned + 1;
    end loop;
    outset.endcreate;
    return odciconst.success;
  end;
  member function ODCITableClose( self in NColPipe )
  return number
  is
  begin
    return odciconst.success;
  end;
end;
/And to use it
SQL> select * from table( NColPipe.show( 'test', 3 ) );
test1      test2           test3
row: 1     row: 1              1
row: 2     row: 2              2
row: 3     row: 3              3
SQL>  select * from table( NColPipe.show( 'two', 5 ) );
one        two
1          row: 1
2          row: 2
3          row: 3
4          row: 4
5          row: 5
SQL> select * from table( NColPipe.show( 'one' ) );
one
1
2
SQL> Anton