Problem in truncate/drop partitions in a table having nested table columns.

Question

Hi,
I have a table that has 2 columns of type nested table. Now in the purge process, when I try to truncate or drop a partition from this table, I get error that I can't do this (because table has nested tables). Can anybody help me telling how I will be able to truncate/drop partition from this table? IF I change column types from nested table to varray type, will it help?
Also, is there any short method of moving existing data from a nested table column to a varray column (having same fields as nested table)?
Thanks in advance.

Answer 1

>
I have a table that has 2 columns of type nested table. Now in the purge process, when I try to truncate or drop a partition from this table, I get error that I can't do this (because table has nested tables). Can anybody help me telling how I will be able to truncate/drop partition from this table?
>
Unfortunately you can't do those operations when a table has a nested table column. No truncate, no drop, no exchange partition at the partition level.
A nested table column is stored as a separate table and acts like a 'child' table with foreign keys to the 'parent' table. It is these 'foreign keys' that prevent the truncation (just like normal foreign keys prevent truncating partions and must be disabled first) but there is no mechanism to 'disable' them.
Just one excellent example (there are many others) of why you should NOT use object columns at all.
>
IF I change column types from nested table to varray type, will it help?
>
Yes but I STRONGLY suggest you take this opportunity to change your data model to a standard relational one and put the 'child' (nested table) data into its own table with a foreign key to the parent. You can create a view on the two tables that can make data appear as if you have a nested table type if you want.
Assuming that you are going to ignore the above advice just create a new VARRAY type and a table with that type as a column. Remember VARRAYs are defined with a maximum size. So the number of nested table records needs to be within the capacity of the VARRAY type for the data to fit.
>
Also, is there any short method of moving existing data from a nested table column to a varray column (having same fields as nested table)?
>
Sure - just CAST the nested table to the VARRAY type. Here is code for a VARRAY type and a new table that shows how to do it.
-- new array type
CREATE OR REPLACE TYPE ARRAY_T AS VARRAY(10) OF VARCHAR2(64)
-- new table using new array type - NOTE there is no nested table storage clause - arrays stored inline
CREATE TABLE partitioned_table_array
     ( ID_ INT,
      arra_col  ARRAY_T )
     PARTITION BY RANGE (ID_)
     ( PARTITION p1 VALUES LESS THAN (40)
     , PARTITION p2 VALUES LESS THAN(80)
     , PARTITION p3 VALUES LESS THAN(100)
-- insert the data from the original table converting the nested table data to the varray type
INSERT INTO PARTITIONED_TABLE_ARRAY
SELECT ID_, CAST(NESTED_COL AS ARRAY_T) FROM PARTITIONED_TABLENaturally since there is no more nested table storage you can truncate or drop partitions in the above table
alter table partitioned_table_array truncate partition p1
alter table partitioned_table_array drop partition p1