Collect giving error ORA 22814

Question

getting ORA 22814 attribute or element value is larger than specified type.
TAB1(
item number(10)
item_id NVARCHAR2(250))
SELECT item, tab_to_nvarchar2(cast(collect(item_id order by item_id) as T_NVARCHAR2_TAB),',') as item_list
FROM TAB1
GROUP BY item
CREATE OR REPLACE TYPE T_NVARCHAR2_TAB AS TABLE OF NVARCHAR2 (4000);
CREATE OR REPLACE FUNCTION tab_to_nvarchar2 (p_nvarchar2_tab IN t_nvarchar2_tab, p_delimiter IN VARCHAR2 DEFAULT ',')
RETURN nvarchar2
IS
l_string NVARCHAR2 (32767) := NULL;
-- l_string VARCHAR2 (4000) := NULL;
BEGIN
FOR i IN REVERSE p_nvarchar2_tab.FIRST .. p_nvarchar2_tab.LAST
LOOP
IF i != p_nvarchar2_tab.LAST
THEN
l_string := p_delimiter || l_string;
END IF;
l_string := p_nvarchar2_tab (i) || l_string;
END LOOP;
RETURN l_string;
END tab_to_nvarchar2;

Answer 1

Collect will not work here. Use:
select  item,
        tab_to_nvarchar2(
                         cast(
                              multiset(
                                       select  item_id
                                         from  tab1 t2
                                         where t2.item = t1.item
                             as T_NVARCHAR2_TAB
                        ) item_list
  from  tab1 t1
  group by item
/For example:
SQL> CREATE OR REPLACE TYPE T_NVARCHAR2_TAB AS TABLE OF NVARCHAR2(4000)
  2  /
Type created.
SQL> CREATE OR REPLACE FUNCTION tab_to_nvarchar2 (p_nvarchar2_tab IN t_nvarchar2_tab, p_delimiter IN VARCHAR2 DEFAULT ',')
  2  RETURN nvarchar2
  3  IS
  4  l_string NVARCHAR2 (32767) := NULL;
  5  -- l_string VARCHAR2 (4000) := NULL;
  6  BEGIN
  7  FOR i IN REVERSE p_nvarchar2_tab.FIRST .. p_nvarchar2_tab.LAST
  8  LOOP
  9  IF i != p_nvarchar2_tab.LAST
10  THEN
11  l_string := p_delimiter || l_string;
12  END IF;
13  l_string := p_nvarchar2_tab(i) || l_string;
14  END LOOP;
15  RETURN l_string;
16  END tab_to_nvarchar2;
17  /
Function created.
SQL> select deptno,
  2         tab_to_nvarchar2(cast(collect(ename) as T_NVARCHAR2_TAB),',') as item_list
  3    from emp
  4    group by deptno
  5  /
       tab_to_nvarchar2(cast(collect(ename) as T_NVARCHAR2_TAB),',') as item_list
ERROR at line 2:
ORA-22814: attribute or element value is larger than specified in type
SQL> select  deptno,
  2          tab_to_nvarchar2(
  3                           cast(
  4                                multiset(
  5                                         select  ename
  6                                           from  emp e2
  7                                           where e2.deptno = e1.deptno
  8                                        )
  9                               as T_NVARCHAR2_TAB
10                              ),
11                           ','
12                          ) item_list
13    from  emp e1
14    group by deptno
15  /
DEPTNO ITEM_LIST
    30 ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
    20 SMITH,JONES,SCOTT,ADAMS,FORD
    10 CLARK,KING,MILLER
SQL>  But in general, scrap your code and use listagg (if you are on 11.2) or xmlagg:
SQL> select  deptno,
  2          listagg(ename,',') within group(order by ename) item_list
  3    from  emp
  4    group by deptno
  5  /
DEPTNO ITEM_LIST
    10 CLARK,KING,MILLER
    20 ADAMS,FORD,JONES,SCOTT,SMITH
    30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
SQL> select  deptno,
  2          rtrim(xmlagg(xmlelement(e,ename,',').extract('//text()')),',') item_list
  3    from  emp
  4    group by deptno
  5  /
DEPTNO ITEM_LIST
    10 CLARK,MILLER,KING
    20 JONES,FORD,ADAMS,SCOTT,SMITH
    30 BLAKE,JAMES,TURNER,MARTIN,WARD,ALLEN
SQL> SY.