How deep can we go in levels of nested tables in oracle 12c? - oracle12c

Question

i am trying to do the folowing:
1) create or replace type transaction as object (date Date, description
varchar(30));
create or replace type T_transaction as table of transaction;
2) create or replace type account as object (id int, description varchar(30),
t_transaction T_transaction)
nested table t_transaction store as xxx1;
create or replace type T_account as table of account;
3) create or replace type user as object (id int, descr varchar(30), t_account
T_account)
nested table t_account store as xxx2;
create or replace type T_user as table of user;
4) create or replace table banks (name varchar(20), users T_user)
nested table users store as xxx3;
first 2 types were created successfully, but "create or replace type account..." is giving -> Warning: Type created with compilation errors.
is there an advice for creating such database using multiple level of nested tables ?

Answer 1

Edit:
I did some research on the subject (object nesting limitations) and here are my findings:
According to Database Limits,
every column of a nested table is in effect added to the columns of the host table and the maximum total number of columns in a table is 1000.
So this would be the official upper limit (in case every nested table had a single column).
However, when I did actual testing (on 11g and 12c), I weren't able to create a table with a nesting depth more than 50 because of error
ORA-00036: maximum number of recursive SQL levels (50) exceeded.
Thus I conclude that the maximum possible depth of nesting is 50.
Initial answer:
I am not aware of limits on objects nesting but I think they should be reasonably permissive.
Your code fails because you made a few mistakes:
1. Using type names as column names (date, t_account, etc.);
2. Using nested table clause in a wrong place;
The code should go like this:
create or replace type transaction_type as object (tx_date Date, description varchar2(30));
create or replace type transaction_tab as table of transaction_type;
create or replace type account_type as object (id int, description varchar(30),
transactions transaction_tab);
create or replace type account_tab as table of account_type;
create or replace type user_type as object (id int, descr varchar(30), accounts account_tab);
create or replace type user_tab as table of user_type;
CREATE table banks (name varchar(20), users user_tab)
nested table users store as xxx3 (
nested table accounts store as xxx2 (
nested table transactions store as xxx1
));
Checking
INSERT INTO banks VALUES (
'John', user_tab(
user_type(1
,'regular user'
, account_tab(
account_type(1
,'regular account'
, transaction_tab(transaction_type(
trunc(sysdate)
, 'regular transaction'))
))
)));
SQL> SELECT *FROM banks;
NAME
--------------------
USERS(ID, DESCR, ACCOUNTS(ID, DESCRIPTION, TRANSACTIONS(TX_DATE, DESCRIPTION)))
--------------------------------------------------------------------------------
John
USER_TAB(USER_TYPE(1, 'regular user', ACCOUNT_TAB(ACCOUNT_TYPE(1, 'regular accou
nt', TRANSACTION_TAB(TRANSACTION_TYPE('04-APR-18', 'regular transaction'))))))
Selecting nested table columns
SELECT b.name, u.id, u.descr, a.id, a.description
FROM banks b, table(b.users) u, table(u.accounts) a
WHERE u.descr = 'regular user' AND a.description = 'regular account'
NAME ID DESCR ID DESCRIPTION
----- --- ------------- --- ----------------
John 1 regular user 1 regular account