With a federated database system, you can access and manipulate
large objects (LOBs) at remote data sources.
A federated system supports SELECT operations on LOBs
at DRDA®, Informix®, Microsoft SQL
Server, Oracle, and Sybase data sources. For example:
SELECT empname, picture FROM infmx_emp_table
WHERE empno = '01192345'
Where
picture represents
a LOB column and
infmx_emp_table represents
a nickname referencing an Informix table containing employee
data.
A federated system supports SELECT, INSERT, UPDATE, and
DELETE operations on LOBs at the following data sources, using the DRDA wrapper:
- DB2® for z/OS® (Version 7 or higher)
- DB2 for System i® (Version 5)
- DB2 Database
for Linux, UNIX, and Windows (Version
7 or higher)
The read and write operations supported by
DB2 Database
for Linux, UNIX, and Windows are
listed in the following table:
Table 1. Read and
write support for LOBs| Data source |
Type of operations |
|---|
| DB2 for z/OS, DB2 for System
i, DB2 Database
for Linux, UNIX, and Windows1 |
read and write
|
| BioRS |
read only |
| Informix |
read only |
| JDBC |
read only |
| Microsoft SQL
Server |
read only |
| Oracle (NET8 wrapper) 2 |
read and write |
| ODBC |
read only |
| Sybase |
read only |
| Teradata |
read and write |
| Web services |
read only and bind-out for CLOB
only |
| XML |
read only |
Note: - DB2 for System i (Version 5 or later)
is required for LOB support.
- To run insert, update, and delete operations on Oracle LONG columns,
you need to migrate the remote columns from LONG to LOBs and recreate
the nicknames.
|
- Teradata LOBs
- Teradata LOBs are slightly different than DB2 LOBs.
Teradata does not have any data types as large as the LOBs supported
in DB2 for Linux, UNIX, and Windows software. However,
there are some Teradata data types that can be up to 64000 bytes long.
These data types are CHAR, VARCHAR, BYTE, VARBYTE, GRAPHIC, and VARGRAPHIC.
These Teradata data types are mapped to DB2 LOB
data types when the length of the Teradata data type exceeds the limits
of the corresponding DB2 data type. However, you cannot
apply LOB write operations on LOB columns that are mapped from Teradata
non-LOB columns.
- LOB lengths
- Some data sources, such as Oracle and Informix,
do not store the lengths of LOB columns in their system catalogs.
When you create a nickname on a table, information from the data source
system catalog is retrieved including column length. Since no length
exists for the LOB columns, the federated database assumes that the
length is the maximum length of a LOB column in DB2 Database
for Linux, UNIX, and Windows.
The federated database stores the maximum length in the federated
database catalog as the length of the nickname column.
