use pipelined function to get result set from multi-tables join - oracle

Question

i want to create a function to get selectivity of a table, the input parameter is owner and table name, i searched and find pipelined function can be used here, i used the following codes but i get error for creating function,
create or replace type ROW_TYPE as object
(
column_name varchar2(128),
num_rows number,
num_distinct number
);
/
create or replace type TABLE_TYPE as table of ROW_TYPE;
/
create or replace function getSelectivity(owner in varchar2, tab_name in varchar2)
return TABLE_TYPE
PIPELINED
IS
BEGIN
for myrow in(
select a.column_name,b.num_rows,a.num_distinct
from dba_tab_col_statistics a, dba_tables b
where a.owner = b.owner and a.table_name = b.table_name and a.owner=upper(owner) and
a.table_name =upper(tab_name)
)loop
pipe row(ROW_TYPE(myrow.column_name,myrow.num_rows,myrow.num_distinct));
end loop;
return;
end;
/
error：
SQL> show errors;
Errors for FUNCTION MOVIL.GETSELECTIVITY:
LINE/COL ERROR
-------- -------------------------------
9/88 PL/SQL: ORA-00918: undefined column
7/14 PL/SQL: SQL Statement ignored
12/20 PLS-00364: Invalid usage of Loop index variable 'MYROW'
12/2 PL/SQL: Statement ignored
but if i just query one single table, then everything is fine,
create or replace type ROW_TYPE as object
(
column_name varchar2(128),
num_distinct number
);
/
create or replace type TABLE_TYPE as table of ROW_TYPE;
/
create or replace function getSelectivity(owner in varchar2, tab_name in varchar2)
return TABLE_TYPE
PIPELINED
IS
BEGIN
for myrow in(
select a.column_name,a.num_distinct
from dba_tab_col_statistics a
where a.owner=upper(owner) and a.table_name =upper(tab_name)
)loop
pipe row(ROW_TYPE(myrow.column_name,myrow.num_distinct));
end loop;
return;
end;
/
does pipelined function do not support multi-tables joining ?

Answer 1

You can create a view on the tables like the below and use it in your function
create or replace view test_db_view as select
a.column_name,b.num_rows,a.num_distinct,
a.table_name,a.owner
from all_tab_col_statistics a, all_tables b
where a.owner = b.owner and a.table_name = b.table_name
create or replace function getSelectivity(owner in varchar2, tab_name in varchar2)
return TABLE_TYPE
PIPELINED
IS
BEGIN
for myrow in( select * from test_db_view a where a.owner=upper(owner) and
a.table_name =upper(tab_name)
)loop
pipe row(ROW_TYPE(myrow.column_name,myrow.num_rows,myrow.num_distinct));
end loop;
return;
end;
OR you can try using p_owner instead of owner in function getSelectivity parameter