Oracle：将子选择转换为流水线函数？

Question

How do I generically translate a subselect into a pipelined function call?

For example how would I translate this:

select id, stuff from t1 where id in (select unique id from kw where k = 'foo')

to this:

select id, stuff from t1 where id in (select id from table(has_kw('foo'))

Answer 1

Writing the pipelined table function is relatively straightforward

CREATE TYPE num_tbl AS TABLE OF NUMBER;

CREATE FUNCTION has_kw( p_k IN VARCHAR2 )
  RETURN num_tbl
  PIPELINED
IS
BEGIN
  FOR i IN (SELECT DISTINCT id FROM kw WHERE k = p_k)
  LOOP
    PIPE ROW( i.id );
  END LOOP;
  RETURN;
END;

Now, I'm not sure that it would really make a whole lot of sense to use a pipeliend table function here. But perhaps your actual use case is more complicated and a pipelined table function would be more appropriate.