Oracle BLOBs, CLOBs tips

Oracle Database Tips by Donald Burleson

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.