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BLOBs and
CLOBs Creation
BLOB and CLOB
datatypes are created by use of the CREATE
or ALTER TABLE or the CREATE
or ALTER TYPE commands. In fact, they are
created identically to other non-sized datatypes
such as DATE and LONG with the exception of the
LOB storage clause.
Oracle
blob storage requires
usinf the
Oracle dbms_lob
package an easy interface tio Oracle BLOB
storage.
The LOB
storage clause is not needed if the maximum size
of the BLOB doesn't exceed 4000 bytes. Up to
4000 bytes can be stored in-line with the other
data in the tablespace. If the length of the
BLOB exceeds 4000 bytes it must be stored in
either a system defaulted storage (the same as
the default for the table it resides in) or in
an explicitly defined LOB storage area.
TIP:
I suggest
always specify the LOB storage clause, if you
force the system to do a default storage each
time a BLOB or CLOB exceeds 4000 bytes you could
cause datafile fragmentation and performance
problems. The LOB storage clause gives you
control instead of the system.
An example
creation of a table using a Oracle BLOB datatype is
shown in Listing 1. It just as easily could have
been a CLOB.
create
table internal_graphics (
graphic_id number,
graphic_desc
varchar2(30),
graphic_blob
blob,
graphic_type
VARCHAR2(4))
lob (graphic_blob)
store as glob_store (
tablespace raw_data
storage
(initial 100k next 100k pctincrease 0)
chunk 4
pctversion 10
INDEX
glob_index (
tablespace raw_index))
TABLESPACE appl_data
storage
(initial 1m next 1m pctincrease 0);
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