Oracle LOB Storage Syntax
Somebody asked me to post some examples of Large Object syntax. I checked Chapter 9 of the Oracle Database SecureFiles and Large Object Developer’s Guide, and I agree an example or two would be helpful. I’ve provided CREATE
and ALTER
statements.
Here’s a sample CREATE TABLE
statement for a CLOB
, BLOB
, and BFILE
:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | CREATE TABLE item ( item_id NUMBER CONSTRAINT pk_item PRIMARY KEY , item_barcode VARCHAR2(20) CONSTRAINT nn_item_1 NOT NULL , item_type NUMBER CONSTRAINT nn_item_2 NOT NULL , item_title VARCHAR2(60) CONSTRAINT nn_item_3 NOT NULL , item_subtitle VARCHAR2(60) , item_desc CLOB CONSTRAINT nn_item_4 NOT NULL , item_blob BLOB , item_photo BFILE , item_rating VARCHAR2(8) CONSTRAINT nn_item_5 NOT NULL , item_rating_agency VARCHAR2(4) CONSTRAINT nn_item_6 NOT NULL , item_release_date DATE CONSTRAINT nn_item_7 NOT NULL , created_by NUMBER CONSTRAINT nn_item_8 NOT NULL , creation_date DATE CONSTRAINT nn_item_9 NOT NULL , last_updated_by NUMBER CONSTRAINT nn_item_10 NOT NULL , last_update_date DATE CONSTRAINT nn_item_11 NOT NULL , CONSTRAINT fk_item_1 FOREIGN KEY(item_type) REFERENCES common_lookup(common_lookup_id) , CONSTRAINT fk_item_2 FOREIGN KEY(created_by) REFERENCES system_user(system_user_id) , CONSTRAINT fk_item_3 FOREIGN KEY(last_updated_by) REFERENCES system_user(system_user_id)) LOB (item_desc) STORE AS BASICFILE item_desc (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)) , LOB (item_blob) STORE AS item_blob (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)); |
If you attempt to make the CHUNK
size greater than 32,768, it will raise an ORA-22851: invalid CHUNK LOB storage option value
error.
Here’s a sample ALTER TABLE
statement that adds a new large object column to a table. You can’t modify an existing large object column. You raise an ORA-22859: invalid modification of columns
error when you try it. If you need to make modifications, check this post form last year on re-organizing LOB indexes.
1 2 3 4 5 6 7 8 | ALTER TABLE item ADD (another CLOB) LOB (another) STORE AS BASICFILE item_clob (TABLESPACE users ENABLE STORAGE IN ROW CHUNK 32768 PCTVERSION 10 NOCACHE LOGGING STORAGE (INITIAL 1048576 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645)); |
This all makes sense, but hold on there’s a potential problem when you add a large object column to a table. I’m not sure it’s a bug but I’ll probably open a TAR on it later in the week (arghhhh! I once worked in Oracle Support. :-)). Anyway, here’s what I found:
If you drop and recreate the table, you can encounter an ORA-01430
error. It appears that the large object is really hanging out in the catalog. As soon as you try to re-add it, you get the error.
If you describe the table after recreating it, you’ll see the following:
SQL> DESCRIBE item Name Null? Type ----------------------------------------- -------- --------------- ITEM_ID NOT NULL NUMBER ITEM_BARCODE NOT NULL VARCHAR2(20) ITEM_TYPE NOT NULL NUMBER ITEM_TITLE NOT NULL VARCHAR2(60) ITEM_SUBTITLE VARCHAR2(60) ITEM_DESC NOT NULL CLOB ITEM_BLOB BLOB ITEM_PHOTO BINARY FILE LOB ITEM_RATING NOT NULL VARCHAR2(8) ITEM_RATING_AGENCY NOT NULL VARCHAR2(4) ITEM_RELEASE_DATE NOT NULL DATE CREATED_BY NOT NULL NUMBER CREATION_DATE NOT NULL DATE LAST_UPDATED_BY NOT NULL NUMBER LAST_UPDATE_DATE NOT NULL DATE |
Also, if you run the following query with the DBMS_METADATA
package, the column doesn’t exist in the table defintion:
SELECT dbms_metadata.get_ddl('TABLE','ITEM') FROM dual; |
If try to run the ALTER
statement to add the column that doesn’t appear to exist, you’ll get the following message in Oracle 11.1.0.7.0:
ALTER TABLE item ADD (another CLOB) * ERROR at line 1: ORA-01430: COLUMN being added already EXISTS IN TABLE |
If you rerun the DBMS_METADATA.GET_DDL
query, it’ll be there in the table definition. Also, in its non-existence but existent state (ghost-state), there’s nothing in the DBA_LOB
, or DBA_SEGMENT
views. You can find a query to check large object segments and indexes here. My questions is where has it gone, why is it there, and did I do something wrong because this looks like basic functionality.
If you know the mystery or the existence of a bug, please post a comment.